1986 5.0 gt tranny/engines swap info needed

hello  i have a 1986 5.0L gt(hatchback) and im looking at a new tranny as im planing to put a 450-500 hp motor in the car.
it currently has and automatic and i would like to swap for a stronger automatic,what kind of automatic do i have? and what kind should i be looking at? . ( i do not know how to tell witch tranny it has it goes{P-R-N-OD-D-1})

also if you have a motor build thats running around 450-500hp to your wheels my price range for engine parts is 4000.00-$5000.00please post it with your rearend gears , as i have a macheinest avalible to do boring/porting but i do not know about clearance issues of parts in motor so i cannot collect part numbers for my build because of that lack of noledge and with that im hoping that some one here can give me a hand in chosing the right combination.

Thanks
Ryan Harder (AkA Tha Chronic)  

most likely you have a 4 speed aod, that is what i pulled out in my 89 5.0
you can find places that will rebuild it with all new racing parts and new torque converter, or just get a rebuild kit that can withstand that much hp