Norton Commando 750 breather?

That engine, the crankcases at least, seem to be from an earlier Commando than '72. Both the things in the pictures are engine breathers but a 72 bike should not have the one at the front and the rear one should be at the bottom rear of the crankcases, although people do move them to where that one is. Are you sure the engine number is same as frame number as the number on the picture is an earlier number.

This engine appear to have 2 breathers. The Atlas type on the end of the cam shaft should need to be removed when the one at the back of the timing case is fitted. When you remove the Atlas one you are left with a fine threaded hole. A good 'bung' for this is the clutch adjustment screw.

The front breather is NOT home made, it is standard ATLAS as fitted to the first Commandos up to a specific engine number. There is no engine damage with extra breathers but what will happen  I do not know.

Vin plate looks like it's been tampered with.
 

The breather behind the timing cover has been added, its position I understand is adequate.
The Atlas one is factory original.

The breather on the back of the timing case looks well done and, at a guess, incorporates a positive crankcase ventilation valve (PCV). You can search on here for discussions of PCVs on Commandos. The breather at end of the camshaft is timed which is supposed to have the same effect as a PCV (but doesn't).

As the Commando evolved, the breather moved around until it finally ended up on the back of the timing case, i.e. where yours is fitted. If it were me, I'd blank off the one on the end of the camshaft and rely on the one in the timing case.

Looks like your additional breather uses the parts which Norton used when the breather moved to the back of the crankcase.
This page from AN shows the component parts, including the sponge/foam:

https://andover-norton.co.uk/en/shop-drawing/34/engine-crankcases-crankcase-breather-tachometer-drive
 

That's disappointing. I was expecting at least a flapper valve in there. I'd throw the bits of sponge away and leave it open like the late 850s.

Wouldn't take much to adapt what you have to incorporate a valve.
These BMW reed valves https://www.motorworks.co.uk/crankcase-breather-valve-ena35712-2.html are popular with some people. 1.25"(!) diameter x 0.5" overall height

Not sure about the '71 cases, but the '73 750cc cases do not have any venting holes from the inner crank case to the timing side. A breather plonked onto the timing side then cannot breath & will cause a pressure build up. I would check first.

I don't think the first hole can breath. I did not have one above the timing chain, as you do, so that will probably do.
I bought mine with the breather in the same place as yours, being a popular mod at the time. Head gasket kept leaking & couldn't seem to cure it. Changed it a few times until I found the problem of over pressurising. Put the breather back to the back of the crank case & all was good. Only thing is, that is when it has wet sumped, it would push all the oil up through the breather. 

There's a mountain of information about this subject, but that's the problem. Most of the information doesn't quite apply to you if you have the cases with the timed disk breather on the end of the cam. So having been through this mountain myself maybe I can save you the time. Adding another breather is popular because the general concensus is that the one on the end of the cam can't quite cope. It's important to decide if your adding another one or replacing the original cam end one. As long as the timed disc set up still exists on the end of the cam and still works then it's best to keep it in addition to the new one on the timing side.   Sometimes owners replace the cam (which fail often) with one which does not have the machined end to accommodate the timed disc set up, so although it appears to be the standard set up, there's actually no disc in there. You need the disc and you need to know if it's there or not. If it is there then this is good. However, as Gary pointed out, plonking another breather on the timing side isn't enough and although you do have one orifice into the crankshaft chamber (compared to later cases which do not have this one), this isn't enough.  You need to add some/one, otherwise the added breather, which has opened the timing case to the athmosphere, can allow oil to flood into the timing chest and sometimes even up and out of the breather. Before it was added this can't happen as the timing case is closed and thus slightly pressurised. Also, of course, you need the added air flow passage. There are many drawings showing you where to drill the hole(s), which size and how many. Andover Norton offer one (attached) for the combat, but the combat cases are different from yours. Jim Comstocks' website will find you a design, but it is intended for a racing engine and the cases are peppered with 12mm holes, as is the very clear example on the Mick Hemmings engine rebuild DVD.  However, if you calculate the surface area of both of your breather pipes added together and calculate the area of the gaps in the timed breather discs and add that to the surface area of the hole you already have in the timing case near the cam (the other hole you arrowed is an oilway) then it's only really an advantage to add one more 12mm hole to get the maximum breathing advantage. I've attached photos of mine where you can see the added hole (sorry cant do arrows just now). There are options for the placement, but it must be well above any possible oil level. Once this is all done you will need to install an efficient positive crankcase ventilation valve on the new breather pipe to get the very best out of it. Hope this makes sence and helps. Sorry if its a bit long winded. 

most people put one higher up near the oil tank, on that timing case pipe. Partly for aesthetics.
   There are also replacement large sump plugs, if that is what yours has, with built in reed valves, which can cope very well with emptying a fullish sump on start-up. 

However, beware of this very expensive sump plug/breather as it won't fit in front of the frame crossmember by the sump plug on the early Commandos. 

yes, they are in line, although some have in-out at 90 degrees, which is often helpful when sited near tank. No photos, but not hard to find, see accessnorton threads.

Here are pictures showing the fitting of PCV valve (supplied by Holland Norton Works) fitted to my 1972 Fastback. The inlet side is fed from the standard elbow on the back of the crankcase.

The bracket replaces the timing chest breather elbow fitted by a previous owner, to little avail since they neglected to provide the necessary communication with the crankcase …
 

one of the better options, as you don’t have to operate anything manually. Colorado Norton produce it, and they have an vg reputation and have been using them for years.