When anyone mentions 'crate' motor, the first thought with Pontiac owners is, crate = small block Chevy. Nay say I to that idea. SBC's are for Chevys.
There's nothing wrong with the 350 poncho's. Rebuilding one with the right cam, intake and carb you have an HO. I know how much you want to DRIVE your 'bird, my convertible has been laid up for a year now. Thankfully I have my cammer to tool around in.
Keeping it as original as possible will help the value when it has to change hands. My convertible no longer has the original 400, and that has some impact on when I have to let it go. That's a couple of grand I'm missin' out on. Don't loose sight of the long haul.
$5,000 should get you a very healthy rebuilt original mill. If you want FI, ping John (hammered) about the process. Also Jared did that mod to. He's on the FGF list (e-mail). FI will cost extra I imagine.