To me it looks like they used the stock (likely used) rockers and pushrods, and I bet what they did was adjust the nuts too tight so that the rockers were tight on the pushrods. What that will do is make the moving parts in there get peerrty hot and wear out real fast. Thus, breaking the rockers and you could be revvin her higher than those little rods are used to. Check for how much preload has been set on the lifters. Hmm, forgot to ask, what kind of lifters are they? I would assume just hydraulic units? In which case a good amount of preload is to tighten the rocker nut down while turning the pushrod between your fingers. When you feel a slight drag while turning the rod then stop tightening and go about 1/4 turn more. Some people say 1/2 a turn, some say never go half a turn. If you already knew all of this then I would just tell you to go out and buy some good rockers and pushrods. Not to mention that if the head is already machined for screw in studs then guide plates (the proper style!) would only be a quick bolt in thing, but make sure you adjust them for both rods at the same time, and make sure to put some sealer on the threads as they likely go into water jackets. Ask the guy if he ever milled the block or the heads if you can contact him. If he did you will have to shorten the pushrods to get proper geometry. I would just be thankful you didn't break retainers like I did yesterday...that cost me about 3-4 bent valves for sure. Another thing to keep in mind is that a excessively bored cylinder wall will not dissipate heat as well and you could generate some more heat issues with that beast. Hope this helps, good luck