Marc944T

I have an 86 951 and i am going to put in a 87 transmission with lsd. I got this for free and i toke my 951 off the road for the winter so i would like to put it in soon. The only problem is that i need a reverse because it is broken. It has to be a original 87 transmission because an 87 is a little bit bigger than an 86 reverse. Any info will be a huge help.
Thanks
Marc