Click for pics
The rubber bumpers on the bottom of the seat are different, just change them around to fit the subframe. The Early TBird (95-98) and the TBS subframes are pretty similar, The TBS one is bent upwards
to accommodate the greater suspension travel of the TBS rear shock.
You can see in the photos the location of the latching mechanism is different and it is rotated 180 degrees. Very Early TBird seats do not have the second location for the latch built in so it's not as easy to switch them, but it is still dooable.
The newer TBird seat is bolt on and it is quite different, it is like the legend seat with different padding/covering. it's possible to install the locking seat on a later TBird. Search Mick's old (about 3 or 4 years ago) posts and you'll find some info about that, if it's still there.