this may be completely un-needed advice, in which case I apologize for wasting your time but I remembered something in the course of assembling my own heads yesterday that has been a cause of grief for many.
Your rocker shafts need to go on such that the punch marked end is upper most in order that the oil feed via the upper studs can lubricate the needle rollers.
If your engine has not run for some time, you should move the rocker shaft down about half the length of the rollers and oil them up so that they are adequately pre-lubed, it is also a good idea to ensure that the oil feed is working as soon as possible after first start.
And, if like me, you have a momentary lapse of concentration whilst applying the start up lubrication and end up with needle rollers all over your work bench. A clean plastic lid with a small quantity of lithium grease smeared in it is the go - after you wash the rollers in solvent put them on the grease smeared lid and work them round a bit, you only need a hint of grease on the rollers and they will stay in lace as you laboriously put them all back in the race.
To anyone wondering, you have the right number of rollers in the bearing when there is a little bit more than one roller's worth of space left, in other words you could put one more in, but not two - that is the way they are designed.
