There are 12:1 gear boxes that will not require changing hoses. I put one on my car when I restored it. I want to think its from a mid 70's trans am. It made a big difference in the bird.

I just changed the box in my son's 75 Chevelle from a variable to a 12:1 also. It is being hooked to an ls1 engine so I went with a later year to get the newer style hose fittings.