my advise = dont go with the 95 riv for a donor car its series 1 and has almost no aftermarket support , you want series 2 which started showing up in 96 in rivs ,bonnies ,park aves etc... but had a 4t60 trans and a pcm that doesnt have a lot of tuning support.
starting in 97 all that changed and the sc cars all had 4t65e-hd trannys and pcm's that are fairly well supported. you can find these drivetrains in pontiac gtp&ssei , buick regal gs & park ave ultra , olds LSS , as well as in some impalas & monte carlos , hopefully I didnt miss any.
why you would want to go with this if you choose the FWD path is because the series 2 shortblock has withstood 8.6 @159 on stock factory assembled block/rotating assembly (zzp fwd grand prix) - its pretty stout.
the same series 2 3800 has also been 8.9 @15x in rwd configuration in a firebird (intense racing)
also the fast honda drag guys you will see swap trannys to the 4t65e- hd becuase parts are available to tolerate up to around 1,000 hp - but they arent cheap at that power level , 500-600hp is more often seen in series2 3800 race cars and 3-4 grand can build one to tolerate that power level , stock trans are marginal in a 12 sec full weight car or 11 sec in a lighter chassis like the ones you see in fieros - hook hard and you will be looking at a drive chain and input shaft upgrade in your near future