Sounds to me like the timing maybe ever so slightly out - I know on mine when I do the timing I've got a TDC groove on the flywheel which you can see through the gap where the flywheel sendor is.

Only other thing is that possibly one of the new valves are sticking on that cylinder. But having said that it still should start just on three cylinders - which leads back to the timing being ever so slightly out. Also 8v engines can be a pig to start the first few times after they've been apart - try sticking a little bit of petrol in the inlet manifold to help it fire up - normally works for me.

HTH!