3-speed
The three speed that would have come in your car is the A230 heavy duty three speed. It is about the same size and weight as an 833 four speed. In other words, it's BIG, HEAVY and STRONG.
They do not compare in any way, shape, form or fashion to the earlier six cylinder only three speed transmissions. The A230 is a strong BEEOTCH. Lots of drag racers used them. They are hard to break.
...and no, they are not rare. What happened through time is dumbasses swapped four speeds for them and scrapped them. They are fine transmissions.