273 rocker info please

He is wants to run the factory 68 4 speed cam. Assuming he has the 340 rocker system all he has to do is inspect the rockers and shafts, drop the pushrods into the lifters and bolt them on.

Not saying you are wrong, but how much will he gain with perfect preload after spending how much money and the time to do it correctly?
And that's great. He can certainly do that and probably run for a very long time and never have issue. But is that what he wants, or does he want the valve train geometry to be correct? Because I can just about slap guarantee that even the stone stock valve train on his engine was not correct from the factory. If any of them were, it's just because of chance. Yeah, they'll run 100K miles or more not "correct", but if you doing a build, why not get it right? Why not get the rockers in the correct place on top of the valve stems instead of on one side or the other? Why not optimize valve tip, rocker arm, valve guide and valve stem wear? And it's POSSIBLE you might pick up a tic more power by reducing friction. If you're leaving something 100% stock and unmolested, yeah, ok, run it. But if you're doing a ground up build, why wouldn't you want it right? There simply are no down sides.