Any Saginaw 4 speed would have better gear spacing than your 3 spd. A high first gear is ok, but if it's too high like more than 3.09 ,your car would most likely not boost too much in first gear, (not much of a load on the engine) especially if you install a turbine A/R of .96 or higher.
So , if you keep your 3.23's through 3.55's a first gear of 3.09 is fine.
I just like automatics when it comes to turbos's, you can brake stall them & launch w/boost, much easier than a car w/manual trannys.