1982 pontiac firebird general questions?

[unerismy]

i have and 82 pontiac firebird thats a restoration project. its got a 305 with a turbo 350 transmission in it, (it had a 350 but i blew it up) its only a 3 speed and doesnt have enough gear for me to go as fast as i want. its a 3 speed tranny, and has a 10 bolt diff. i was wondering wat would b a good set of gears for me 2 put in it to atleast go 100-120, i dont wana replace the transmission either. Now another question, ive got my heater to work, but it only blows out the defroster and wont change when switched, i duno if this is a vacuum line or how it works, but any info would b helpful. Thanks