Everything that fits a GP, Bonneville, Impala, Regal, Park Avenue etc motor/transmission will fit your Riv.

Only thing you need to consider is if it's a 96, then the trans is a 4T60 instead of a 65. Many headers have clearance issues with where the 96 connector is located.

Drop a set of drag bags in the rear end and you'll stop having so much weight transfer.