Bill,
I would go with the 350, since it's already being built. Plus you'll have much more power potential and it'll be easier (and cheaper) to find hop up components. If you stick with the 250 you'd have to go with headers if you go with a non-integral head. The headers to fit your truck can be had cheap - I even have a spare set to fit 63-87 Chevy trucks that I'll let you have for cheap. Especially if you'll sell me another cherry picker.
:p
-magic mike-
