All Pontiac V8 engines fully interchange - makes no difference which one you drop in. 350 Pontiacs are cheap and available. You can drop in a small block Chevy, but you'll have to swap out the bellhousing (or tranny if auto) and do a bit of work with wiring and plumbing (starter and fuel pump on Chevy is on the opposite side from the Pontiac). So for a quick temp swap, you need to stick with a Pontiac engine. Any of them will bolt in identically.