My experience with these has been mostly with the 331 in my vintage dirt modified, which has quite a few modifications. I will add a couple of things, The first is that I have adjustable pushrods with an old Engle roller tappet cam. A lot of people don't like adjustable pushrods, saying they are difficult to adjust. I have found that they are no problem if you heat and bend a couple of wrenches just for that purpose. The second is that I originally ran a rebuilt stock rocker assembly with this setup. I broke an exhaust rocker arm the third time out. I was lucky enough to find seven Donovan forged exhaust rockers at a swap meet a couple of weeks later, which I bought for $35. I later found another for $75. Still, $105 for a set of Donovan's? I'll take that every day. Haven't had a lick 0f trouble since. I do try to keep the rev;s below 5500, because this is vintage racing and I don't want to build this engine again.