A body A833 4 Speed transmission

As for the overdrive box and power;
I put 330 hp into it for a about 4 years, and then 430 for another one.
The ONLY weak link in that box is the teeny tiny M/S overdrive gear, which for me I broke two of them before I finally swapped to the Commando.
If I was to ever use that box again, I would put an interlock on that od-gear, to remind me to back off the throttle. After the first one exploded, I bought spare transmissions.

As for the B&T; on the street, it should be, fine if you have it.
I think if anything, the 7260 joint at the back is the first failure point, and the thinwall driveshaft is probably the second . and of course, if there's still a 7.25 back there, and no posi; that's just a ticking time-bomb.

BTW;
@toolmanmike says 66 was the first year of the slip yokes.