There is the difference between the /6 and the V8’s.
Mostly all ’76-89 FMJ K-frames are the same, but there are a few minor differences between the years. Not anything to make them not interchangeable.
Oddly, Chrysler had a different part number for the K-frames each year.
The differences I see is one might have a slightly different welded in bracket, and next might have more welds in same area. The next one might have 2 pieces for this corner and next has 3 pieces for that corner (welded in). Minor things like that – but again, nothing to affect interchangeably.
BudW