Too much Oil in the head - smoking exhaust

Having sorted out the clutch with a new spider and new engine sprocket with a bigger offset I can now turn my attention to the engine which has had a rebore and new piston. Compression is good but after about 30 seconds running it starts to smoke - seriously smoke! and oil is visibly dripping from the exhaust on to the timing case (high level exhaust). So I whipped the head off to have a look. There was a lot of oil around the valves and also on top of the piston. Both ports were covered in oil too. On inspection I could see that the bottom collars for the springs were made from ones with a smaller diam for the guides and filed out (badly) but in any event they almost completely block the drain holes (which I made sure were clear) Does anyone have a bottom valve spring collar for the Wellworthy head they could look at, does it have any sort of machining or chamfer to enable the oil to drain freely away? I thought about adding a small shim to lift the collar a little but didnt have anything the right size. I installed an o ring on the valve stem to try to hinder any oil flow down the valve stem and reassembled. It seems to have improved but I still think it isnt draining away well. Smoking was reduced when I cut off all oil supply to the head for a little while.

So if anyone has a bottom valve spring collar/seat they could post a pic of the underside of so I can see how the oil gets past to the drain hole I'd be very grateful!