Need help asap 340

The rockers may have been well worn before and they were pushed to their finish by a bit more stress. My concern would be that weak/worn parts like this are also in the bottom end.

For minimal $$, I wold try to check out the bottom end, and redo the top. But to know the bottom end is right, it HAS to come apart and be thoroughly measured, all parts checked. Basically, starting over is the only way I would approach this; back when I was young and poor; I would take a chance on the bottom end. The bottom end may well be perfect, but there is no way of knowing this at this point. And you don't know how it might have been abused by the prior owner.

$10K is a LOT in my world; my son and I just built a 340 from scratch at 375-400 HP (supposedly) for a bit over $5k with goods heads (Edelbrocks); all we had was a crank, oil pan, headers, and timing cover to start with LOL. So all else was bought. But we did all the checking and assembly and just used machinists for that work. I am guessing you are not as experienced a builder, and so going to someone good with your pile of parts may be the best bet. I cannot make a direct endorsement of MRL (As I do not know them personally nor even have had them do work) but he seems to enjoy a good reputation here, and is close to you, up in MI. There are also a couple of older, good builders in the Toledo area; both have built serious drag race engines for years. PM me if you want numbers.

450 500 HP... how did you come by that number? 350-400 HP is easy in this day and age. 500 is more work and more serious parts. What are the intended uses for this car? Drag racing? Cruising? ALWAYS start with the intended use and then build the engine to that, NOT to some good sounding HP number. I ask because all to many new folks think that 500 HP is needed for some reason...but 350-400 HP can be a TON O' FUN on the street if built in the right way and is significantly less costly.