This may be off topic, but here's a couple of cheaper alternatives...
Chrysler had an overdrive transmission (three speed with fourth being OD)in the 70s. It looks just like an A-833 four speed, but has an aluminum case. It bolts right in with a minor mod to the trans and no mods to the car. You may have to find the correct bell housing. The gear spacing is strange though-it has a low first gear and then a big jump to second. Imagine skipping second on a normal four speed.
Another possible solution is the four speed OD gear set from Passon, which solves the "big jump" problem.
Good luck

While outside on the turnpike They got this new hit tune Where thrills become as cheap as gas And gas as cheap as thrills