Were the heads milled? Usually on older builds,most people mill the heads fron.020 to .080.Then order adj.pushrods/different length pushrods.Check it out.Call Hughes/Comp cams,and order a adjustable pushrod. They(or here)can walk you through it.
If we're talking about a rocker shaft setup such as a LA, B, or RB engine uses pushrod length has no bearing on valve tip geometry which is the problem the OP says he has. The only things that affect valve tip geometry is valve stem height, rocker fulcrum height, and the rocker arms themselves.
