Passon or Tremec TKO 5 speed gear box consideration.

For gear vendors and 4 speed you need to change over to a "b" body mainshaft and use their tails haft housing. Shorten driveshaft which I have read is not optimal for unerversal joints. (Don't quote me)
Also heard it's not good for switching at high torque or horsepower areas and you will never shift from 1 to 1 od then 2 then 2 od etc. So the shift split is a moot point.
I like the t56 idea more and more with 6 gears all contained with one high price. I believe you are at same price range when going for t56 and gear vendors