I am working on a friends 1985 300sd and the front seats are shot, I found a nice set in a 1986 300E anyone know if they will fit?

You would need to swap the bottom pan, which isn't too hard to do, but you need to pop up the springs from the bottom. Hit in between the springs with a hammer and punch (air hammer preferred...much faster/easier). Then you can slide the w124 pan out, toss it aside and put in the factory w126 pan that is already in your vehicle. You'll need to hammer back in the metal that secures the springs (best to do this with the seat cover and cushion off).

I happen to have both pans on hand. Pics below and you'll see the differences and why the pans need to be swapped