I posted one of the original write-ups of this swap on my site back in '99 or '00, although the original idea wasn't mine.

There are different part numbers because there are small changes in the circuit boards of the different AFMs - even if they look the same externally, there are some subtle differences in the slope of their output signals. As long as you don't mix the "early" style (pre-'88.5) AFM with the "late" style (pos-'88.5) ECU, or vice versa, the AFMs are cross compatible. In other words, it's OK to use a 1987 AFM on a 1986 22RE, but don't use a 1990 AFM on a 1986 22RE, or a 1986 AFM on a 1990 22RE.

As for the larger Supra/Cressida AFMs, the 1982 5MGE AFM is plug-and play, because the output signal runs from low to high. For the other years, the output signal runs from high to low, so as the flapper door swings open more, the output signal decreases, meaning that the engine will run increasingly leaner, exactly the opposite of what you want!! To use one of the 83-85 5MGE AFMs, you need to swap out the stock circuit board and swap in the circuit board from your stock 22RE AFM.

I don't know if this clears things up or makes them more confusing, but that's some of the background story on the AFM differences.