Would the aod 4x4 trans fit in a 79 truck (redoing the trans x member?)? I’m guessing 83-92 type trans?

It depends what transfercase combination you use. I am using a 47rh to an Np 205 and there is no support on the tran/t-case adapter so I will have to make one to the existing cross member on my 78.

Should have said an auto trans. Looked at a friends 79 and it looks like a cast iron hookup to the regular case, but wondering about a newer type (with the overdrive part) if can’t find the 79 one.

Up through 1979 it was a 203 . 80 and newer was a 208 and its variants.

When was the first year for OD?

88 i think. Most trucks will have the NP 208. Around 91 the NP 241 become available. The NP 205 was also available in high gvw trucks.

Either way, it's a very different mounting arrangement than the NP 203 cases used. Grab the od transmission, case and crossmember from the same truck

89 was the first year for OD, If you go with an overdrive trans it will push back the transfer case so both cross members and drive shafts will be needed.

Thanks to both answers, will have to shorten the back shaft since this is a short step side, get crossmember mounts too.

With a short rear driveshaft, you are really going to have to watch the height difference between the rear axle and the back end of the transfercase. You will run out of U-joint movement pretty quickly with a short DS.

On my ramcharger build, the rear yoke ended up within 1/4" of where it was before swap. Went from r big block 727/np203 to 47rh/np205.