Hughes rocker arm pedestal shims

Your real fix is getting the right length pushrods. Smith Bro's makes some great ones. Not cheap, but light-years better than the stock stuff and they'll make them any length you want. I have two sets, one in my 340 and another in the 318 I'm building. The 340 has Harlands, the 318 will be getting stock style 273 rockers.

Shimming up the rocker shafts should work as well, and that will cost a ton less. The shims shouldn't cause you any issues.

But why on earth will your 340 never see more than 4k rpm? Even a bone stock 340 has a lot of fun left in it at 4k. :burnout: