Transmission and drivetrain mods

What mods do you guys recommend for transmission and drivetrain? I have the 4 speed overdrive coupled to a 305. What is the name of the transmission? I mean like TH400R or sumtin, cuz i dont know what its called.

What is a compatible rear end for an 89 caprice, that comes from another car? I heard the camaro/fb TPI cars had a 3.73 rear end with limited slip differentials. Does it fit to the caprice?

What else can i put onto my transmission? So far i have fluid cooler, performance automatic fluid, and shift kit in mind. The rear end will come later, but pretty soon.

All help will be appreciated.

You probably have a TH700R4 transmission... I'd recomend a stall torque converter if yah want it to be quick off the line.

Thm 200-4r

Well...went to parts store and found out ring & pinion + rear end rebuild kit costs near fortune.(for grass root guy like me). SO, my new plan is to go to a wrecking yard and look for a car with an 8.5" 10 bolt, like on my caprice, with 3.73 or higher final gears, and possibly a locking diff. The brand new detroit locker costs upwards of a grand....half the money i will be spending on the car...

BTW, im gona weld the rear end shafts together if i dont find a cheap diff, so itll be fully locking.