727 Tail shaft

Need help,got a tranny from a 78 van (727) to use as a core or rebuild.Was behind a 318 and planning to put in a 340 Duster 400 hp,3400lbs.Does the tail shaft need to be shortened?Just need a very reliable trans. not really for strip, work just need to eat a few stangs ..........if you get my point.Are the gears the same as in cars(ratio)?First time forum user!!!!!