Well one possibility is making a 496 out of that 454, it is fairly common now to do this. It will make more torque and be easier to make your 500-550 horse. Scat crankshafts sells a nice 496 rotating kit. The block will have to be clearanced though, local machine shop can do that. The other big question is what type of cam, flat tappet or roller. That block was not meant for a roller, so u would need a retrofit roller kit. Those aren't cheap but I have seen them on ebay every once in awhile. Flat tappets seems to be too many problems, I think a roller is much better. Make sure you get the block checked out to make sure it isn't cracked and that the bores are good. It will need to be bored/honed/decked true to the crankshaft centerline. Heads u can use stock iron ones, but they are heavy. I have a very nice pair from a LS-6 1971 Chevelle which I was going to use on my Corvette, but I ended up getting some Merlin 3's aluminum instead. Let me know if u are interested. The heads have been magged and blasted clean but need a valve job. One last thing, keep an eye on your compression ratio. You want to keep it in the 9-9.5 range with iron heads, 9.5-10.5 with alum heads. Generally your pistons and heads will determine this, so careful planning here will pay off. Good luck