That is true about the intake. It is a limiting factor in making hp. What is wrong with the block that is junk? I have seen some really bad blocks that could be saved. About the only thing that is usually non-repairable is a freeze crack.
Even though the intake is a hp killer, it will still make 550+ hp NA with a little work. It all depends on how much hp you want to make as to if the intake will work for you.
Eddie

502MPI/EFI are good candidates for prochargers. I had a Baja 272 502 EFI with procharger ran 78 best speed, 76 with a load.

Im going to do a 502 crate engine this winter 415hp and was wondering what the best intake, carb set up would be. I already have brandnew eddie marine headers and long risers. looking for 450-475. Anyway to do this without touching heads, dont want to pull heads off a brand new motor.

Call Bob Madero. his handle i rmbuilder here n OSO.

Tell him what yuo are doing and he will send you cam to install. No reason you can't get 550 out of that engine and those heads. regular 800 carb and a single plane intake of some sort. you will need to change the rocker studs and add roller rockers. Other than that, it is pretty simple. I am finishing that exact thing right now for a customer.

Good luck