Find a shop that can custom build all new gearing and the synchros, a new shifter rod, new input, lay and output shafts. While you´re at it, tighten up the gears a little bit and throw on a B&M Short shift kit with a stage 2 clutch. instant engagement with short throws like nobody´s business. Ever driven a new Sentra SE-R Spec V? that 6 speed gives me a woody just by the way it shifts.
well short of finding a way to bolt up an old Muncie Rockcrusher find a good shop that deals with performance tranny work an tell them what you have. Give them some details to work with - what you have done to the engine and suspension. Don´t forget to let them know how you will be driving the car - howmuch time on the strip and how much on the street. Autocross, Rally, Sleeper, or just a fun daily driver. These guys know what they are doing and will save you money in the long run as long as you are honest with them (and yourself) about what the car will be.