This procedure says use the 13A 50V MOSFETS.
http://www.bmwe34.net/E34main/Mainte...ical/Sword.htm
I think you're good to go.
I'd remove and check the fan motor also. Relube it at a minimum and consider changing the brushes. Motors draw more current as they age, due to bearing issues, loss of brush pressure due to wear can contribute and this is hard on the MOSFETs.
Paul Shovestul