Re: Suggestions for 258/350
Well, all I can say for sure right now is that since you already have a 258 in your rig, it'll be easier to put another 258 in it instead of doing a motor swap. You already have the accessories, etc... to make the 258 work. Why bother swapping to a completely different motor if you don't absolutely have to??
Don't get me wrong, I am traditionally a Chevy guy (and generally in favor of dropping an SBC in anything that moves), but based on prior experience I'd say that sticking with the 258 will give you fewer headaches when you're wrenching. However, the more you modify that 258, the less reliable it is going to be... nothing against the 258 at all; that applies to ALL motors, though... you run an agressive cam, you wear out valve springs. You run more compression, you are more sensitive to bad gas. You run headers, you're more likely to end up with an exhaust leak. That's just the way it works.
Unless you have a line on a good deal (I mean REAL good) on that TBI 350, I'd look into the later model Vortec 350's pretty seriously... they make a LOT more power and are just as docile/reliable.
Honestly, though, if it was me, I'd look into building a one-off mild turbo setup for a (relatively) stock 258. Low boost, stock redline, and PLENTY of power for all but the most extreme situations.
But that's just me, and I'm kinda strange like that...