850 camshaft choice

this has been debated many times , including recently on accessnorton: I suggest reading that one.

…and there is no “right” answer either!

For your spec with a Fullauto and flat top pistons a standard type cam is an excellent choice for power, torque and fuel consumption. Broad power band using twin Premiers, K&N filter and Peashooters. Also works well with mildly tuned or modified 850s in my case.

My cam and measured 8.5:1 compression Fullauto is the Web#312, recommended and bought in 2016 from Jim Comstock in the USA. Modern alternative to the cheaper standard 06-1084 cam but slightly more lift and duration with quiet valve clearances of 0.006" inlet and exhaust.

Drops straight in as per standard using the existing timing marks etc, no fiddling with cam timing required. Either cam would be a good choice. 

https://www.accessnorton.com/NortonCommando/web-cam.21028/

As Jan suggests, been debated to death with many opinions of the "pulls like a train/strongest Commando I ever rode" variety but no dyno runs to back these up. Some that do with special cams like PW3 are not very impressive but probably due to poor engine or carbs setup etc to be fair.

Yes I noticed the valve clearances, no idea why they should be 0.016" standard is 0.006" inlets and 0.008" exhausts. Worth having a word with Newmans or RGM. The Web#312 specs are below to compare. It's a welded cam using an old cam supplied by the customer.

I use a Trispark, not familiar with Rita, best people to ask is Al Osborn or Dyno Dave in the USA who posts here occasionally. May work as is but worth getting it running efficiently if possible, even a 72 year old needs to blow out the cobwebs at times.

Considering the bike now has a FA head with std inlet valves the best cam choices would be 06.1084 and PW3. The reason being without the larger inlets it is not going to rev as high as a 750. It makes sense to utilise the torque and not try increase the HP from the 850 motor, you have less under the curve to play with, and you don't get something for nothing. For road the use the above cams are ideal, even the std cam can get the read wheel to break traction if used hard.