Vacuum on 1968 GTS 340 4 spd.

Ok, turns out my vacuum gauge was messed up. I have 8" of vacuum. And yes I do plan on changing the balancer. So much for bolt on replacement heads if I have to change pushrods and or Rockers. My fault for not checking. I think 1st I might try putting .010 Rocker shaft shims in to see if vacuum changes at all After I do the cam check just to see if there is a change in vacuum . Sadly I never checked pre-load thinking direct bolt on ect: motor wasn't decked .I dont have a sm. blk. adj. pushrod to check preload . But I agree maybe intake valves not fully seating as I cant find an intake leak . Anyone selling some decent 273 Rocker assemblies? I see a few on E-bay. I don't have money to throw around right now but I do have time. I'll order a shim kit and adjustable pushrod for now to check preload. I do appreciate the advice. I'll keep you posted.