Thought I would give you a few more details that I know of. First you can enter 'riviera' on the search below and see some of our previous turbo Riviera discussions, also try 'TH325-4L' search on bottom of trans forum for the same. I am no expert on the TH325 oTH325-4L transmissions but I do know they have a few differences from regular Riviera, Toro, Eldo versions. The ones that came with turbo engines have specific manufacture code "BJ" on identification plate, and run higher transmission line pressures than the other Rivs, and they usually had a 3.15- 3.36 differential attached to them. Any other diferrences I am not sure of. You can upgrade torque converters, not sure if the turbo version trans used a different torque converter. Shift kits also available.
I don't know how much time and effort you want to put into your Riv, the best thing and well worth it would be for you to buy a rough 84-5 T type Riviera that has a good motor and trans in running order, and buy it and convert everything over, or buy a good T Type Riv(84-5) and go from there. The turbo riviera hasa few different parts from a GN/ Regal turbo, headers,crossover, turbo, downpipe, oil pan, motor mounts, are all different. Going the 84-5 YT type Riv route would be far more worth it to you than messing with the 307 for sure. While the 84-5 Rivs are somewhat rare ( approx. 1000 each year) a few good cars for parts or whole show up here in cars for sale section etc. or ebay, not real exspensive, really, shipping could sometimes cost more than car.
Again, check search option for past discussions, maybe someone else will chime in here. By the wayI do have an 85 T type Riv, and 85 Riv drivetrain in another car.
