but why would you want to?
I know you're a smart man and have considered the options, so I'd honestly like to know what your thinking is.
Also, as Mopar Sam mentioned you would have to be very careful with the donor 904, cuz somewhere in the 70s they changed the spline shapes, but not the count. I did not know that, and my swap went 20 miles until I floored and Ziiiing, she stripped all the splines out of the rear planetary. Ok, so now I did some research and figured it out.
Here's the tricky part;
A had many 904s in the shed several that were torn-down, both late and early styles. For the life-of me, I could not tell one from the other. IDK the change-over year but it might have been 1976; mightabin.
BTW the gearing is on that tiny gear at the center of the sunshell, together with the planetaries. If you swap out first, it automatically takes second with it. If you want a mixed gear set, I think A&A has it.