A Rodeo or P'up 3.1 (4WD only) is a direct bolt-in replacement. And likely the 3.1 with cast-iron heads and distributor, found in early 90's GM FWD minivans, is a direct bolt-in also.

I imagine a Camaro 3.1 might bolt in if you drilled starter holes but hardly any point there, you might as well rebuild an Isuzu 2.8 and use 3.1 crank & pistons to accomplish the same thing without drilling.

Also, later models of the Fiero 2.8 V6 are a direct drop-in since they already have the starter mount on the correct side.

A 3.4 is your bet bet for Cost vs. Performance.

HTH..........ed