The '67-'72 was available with the 4.11 gears, and the 3rd memeber is a direct swap into your existing housing. One thing I'd suggest would be to change out the 'Glide, perhaps to a 700R4. That will not only get you better gear range (4 instead of just 2), but you'll gain an overdrive gear which will greatly help in the rpm dept. Combine that with the 4.11 gears, and maybe a taller tire, and you'll have a truck that'll cruise vry nicely w/o overrevving the engine.
