Hey Cole, do you have Jim Hand's book "How to Build Max-Performancs Pontiac V-8s"? If not I suggest you get a copy and read it over. He has a lot of usful info and tips. He also runs a 455 with Iron heads, has thousands of 1/4 miles runs and uses the station wagon as a driver.
What are you starting with 400 or 455? I thought a 4.25" was a tight fit, could be wrong though. Man that's a big crank, IF you can get it to fit you'll be moving a lot of air, more than you can get through a set of 48s, and more that you can get through a performer rpm. I traded out the #48 Ram air III heads off my 428 for aluminium as I had detonation with the 48s. I don't think you can make the chambers big enough to run a crank that size and not suffer detonation with 48s. What would you use for rods and pistons? Then, as Firebob says, what are you going to fuel it with. Listen to Bigchief. Not that I'm trying to discourage you, I'd love to stuff a monster crank into a Pontiac block and have all the necessary parts to have it scream down the track then stop at the A&W on the way home. But I don't have the many thousands of dollars it would take to do it. If you do, go for it.
