I recently got a 1987 toyota supra 5 speed na car. I know of some things i can do for more horsepower.
exhaust, high flow cat, cold air intake, under drive pulleys.
Is there anything else i can get that will help me increase horsepower?

What is the top speed of a supra. Without governers or anything.

And last but not least, can u get a 6 speed tranny for a 7mge 1987 supra? THANKS

i probly wouldn't waste your money on u/d pulleys... or if you really want one make sure they are dampened as they are known to flog out bearings if they are not
you could also get a new set of headers to help that exhaust flow

top speed of a supra depends... if yours is a north american model then i guess it's 130mph or something
if it's got a jdm ecu then 110mph/180kph you hit speed cut ;)

and no you can't get a 6sp trannie for the mk3

gl with the car and enjoy the feeling of a supra owner... and head gasket blower :P