So i was driving my 87 GL turbo, with the part-time (push button) 4wd 5-speed, and my front CV axle had been going out for a while, but finally earlier today did the dramatic "Crunch... POW!!" earlier and wouldn't drive in front wheel drive so I had no choice but to drive home in 4wd (Rear wheel drive) for about 15 miles. It drove the whole way perfectly smooth and it barely made any clicky click sounds around corners

 

my concern is if this could have damaged my front Diff. or the Center Diff??

 

And what transmissions can be easily swapped in, I have an RX tranny, a non-turbo D/R 5speed from an 87 GL, and another non-turbo part-time 4wd 5speed in an 86 DL

Should not have harmed either diff.

There is no center diff, this is 4WD, not AWD

I did this in an 89 GL, it will cause no damage,

I agree, the trans is most likely fine.

Has anyone ever driven it like this for a long period? Will there be any long term damage, like can I remove the toast front axle and drive it like this for a while?

you can separate the outer cup from the rest of the axle and run it rwd. i dont recomend it though. i ruined my driveshaft.

The rear output shaft from tranny? Or the driveline? I just recently rebuilt all three U-joints on the driveline

I had to for a month or two. My front frame was rotted, it was pulling the CV joints apart. Thsi wont ruion your driveshaft unless your driveshaft already has issues from say age. Its akin to say jogging is no good for you since it killed your 100 year old uncle. 

For future reference........if this had been a 3spd auto.......there can be damage to the transfer clutch (4wd rear output) if you do this.

 

The 3at transfer clutch is small, weak....and all of them are 25~30 yrs old.....it won't hold up to rear wheel drive action for long.

 

I had to limp my 84 sedan like that once.........first hill and the transfer clutch started slipping.......made it another 1/2 mile home but it would not have lasted much longer.

 

In contrast.....I drove my 89 wagon from Montana to Oregon pulling a 1500 lb trailer.......in RWD after removing the broken piece of the front axle.