Am I just lucky with my 7.25?

The 904 has been gone through: clutches, bands, shift kit, stall, etc.

Doesn't really matter much (well, it kinda does actually) what has been done to the trans, if the rear end fails with a good driveline shock, the 'sprag' in the transmission can/might/will fail too.
But the problem is, you won't notice that right away. You WILL notice it the next time when the car is ran through the gears and the transmission will literally explode into pieces.

Nice car though.
Get yourself an 8-1/4" axle.