It really depends on what end result you want. If it's just to have a running engine most any 235 would do. I say 235 because there are a lot more of those out there than the 216. However if you want to upgrade your drive train so you can cruise above 45 mph then I would look for a 261, Canadian if you can find one. Those 261's had hydraulic lifters and full flow oil. However the American 261 may have had hydraulic lifters as well. Pontiac used a lot of the 261.

~Jim