Will the seats from an 86 635 fit in an 83 633?

They should, but I have never actually made the swap.

I have and they bolt right up but your 86 is power and 83 is manual correct? If your 83 has power seats too then they too will switch without trouble as the wiring for the seats only change if they have the heat option.

Hi Bluesman
Thanks for the advice. I haven't actually bought the car yet but I have been looking at it. I noticed the seats in it were tired and found some online from an 86 that were in great shape.
Kind of crazy because I don't even own the car but I can't get it out of my head.
Oh well