By the way I'm new here. I have been Faithfully reading these forums for about a year now. I am building an 81 pickup, and remember reading somewhere when someone was asking about this swap. I thought I would post and give my $.02 on it, since I just did it. Trans came from my 87 4-runner.
Of course it bolts to the motor with no problem. The 5 speed is longer, and so the crossmember will not line up with the original holes.
What I'm doing, is I cut the 87 mounts off the frame, and I'm welding them on my 81. There are two holes in the frame, and the crossmember will line up with the back holes. You could also fab your own mount easily with some angle. both your shifter will be a few inches back further. I had to do some cutting on my floor pans.
The 87 front shaft fits perfectly like a glove! I am shortening my rear shaft.
My plans were to fit dual cases, but my AA adapter is on back order until may 11. I'm canceling my order, and getting a front locker instead.