yes all of the 90-94 3.1s will fit. hey, forget the 3.1, get the 3.1 Turbo out of a 90 Turbo GP, or the DOHC 3.4, or 3800 Supercharged v6, they'll all fit
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2000 Pontiac Grand Prix GT coupe -- mine
2003 Pontiac Grand Prix SE sedan -- Dad's
1984 Chevrolet Monte Carlo SS -- Toy
2003 Chevrolet Venture LS -- Mom's
Good luck finding a DOHC 3.4 that's not junk. Would be a nice project, though. Lotta headache with setup. Motor will physically fit, but getting the harness/ECM issues ironed out could be daunting.