I'm not sure what you mean about swaping motors. From what I can find out in Worldpac, the 91 126 has 4 or 6 different motors, maybe. The left and right front are different, the left and right rear are different, the front and rear are different, and the front could have 2 different brands of regulators which take different motors. In other words, good luck.
I looked at the 86 126 and it shows the same thing. The 84 126 is also the same. The 84 is a generation 1 and your 91 is a generation 2 and they show the same thing, 6 different motors. Possibly Workpac is just covering all the bases for all 126 cars and it is up to you figure out which you need.

Paul M

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84 500 SEL (307,xxx miles)