your choice, the V8 would be 20-30hp more depending on year specs - the swap is pretty easy cuz the 283 was optional, and all that's really needed [aside from a good 283] is the repro front mounts available at most vendors, and a rad fan shroud [sits further back than the 6] .... the 283 will provide a bit more power but if you've got the OD, the 235 should do fine .... I personally think the 283 was the best engine GM ever made

Bill