If you are buying an aftermarket block for the upgrade, go to a 421. You can go 434, but it's a bit of a pain. More grinding, smaller cam core, taller lifters.... With a 5000 converter, you can go about
[email protected] on the intake for duration. With that CI you can back down the gear to a 4.56, or 4.88 if 1/8 only. If you have the 200cc iron heads you can make a lot of power with a roller cam, I ran 8.70's with a 406, 260/
[email protected] Crane .625 roller, and a Super Victor intake/800 Holley on those heads in a 1750 lb dragster.