So I definately want to convert the Fleetwood to dual exhaust. What kind of system should I get? I definately want all stainless steel so it shines. Who makes conversion kits for these cars? Educate me on the knowledge of exhaust systems.

cats or no cats?

You might be able to hack an Impala SS setup, but honestly a custom set is probably better $$ spent. I would be doubtful that anyone ever made a dual setup for those cars (bolt on set).

My recommendations:
1. It is a 307. Don't waste $$ on mandrel bends, it won't help that engine anyway.
2. Get 2 1/4" pipe, no bigger, unless you have $ to spend. Jim Hand runs 11.30's with 2.5" duals. And has proven when he was running 12.20's that 2 1/4" tailpipes hurt very little. Big pipes look great though!!
3. Are you keeping the cat? You can get the diesel pass side exhaust pipe blockoff (for RPO NM8) from a Detroit Diesel dealer, they bought all the GM Diesel stuff. Factory fit for the trucks with the 5.7L Diesel (Olds Diesel). Then you have true duals.
4. Run both pipes down the pass side channel for the factory cat. Then split it up into pipes on each side fo the car.
5. Mufflers depend on your taste for noise. I would go with a good set of borla's if $ is no object. If it is, a set of (if they still make them) Thrush truck turbos. They make nearly as much power as a straight pipe and were around $20 each. Hard to beat.
6. Stainless pipe doesn't come shiney, you have to polish it. So polished tailpipes might be $$, unless you do it yourself. Still can be timeconsuming.

Smack anyone who tells you that you NEED backpressure. If they do, recommend they get Edelbrock's book on engines. Read the theory on exhaust and then they will rethink it. The exhaust port has tons of backpressure, you never want to ADD anymore.

Headers are out there. I would look for a set from a 79 T/A with a Olds 403. Oversize ports are actually a good thing here, the reverse pressure wave in the exhaust that comes back will hit the port walls (and not go up into the port to the chamber) because the pipe is bigger, will help power. A friend of mine did some testing with it. Was very promising!

I waas thinking of getting a set of cat backs. I really want them for mileage, performance, and sound.