Now that I have the facts, I can give you some more information.

Your 1985 745 diesel does not have ABS, and has a 12 count tone ring in the rear end. This tone ring is the input to your speedometer. Your 1992 car has ABS and has a 48 tooth tone ring. The tone ring in the later car gives input to both the speedometer and ABS systems. Some of the earlier ABS equipped cars had a 96 tooth tone ring.

If you install the earlier rear end in the 1992 chassis, you'll have a speedometer which reads 25% of true speed, an ABS light that is always on, and a non-functional ABS system.

You can either change the tone ring which is a big job, or buy an Electronic Ratio Adapter. This will make the speedometer read correctly, but may not correct the ABS problem. The manufacturers of electronic ratio adapter often have disclaimers for using their product to correct tone ring signals for ABS systems.
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john