I CHAGED MY MIND - the 91 sep plate has been drilled for a huge 2-3 shift (I can see in the pic) - I don't like it. SInce you say the 3/4 is blocked ANYWAY, go ahead and bolt the 87 vb on AS IS - once we get straight, we can mod this VB and go on if you wish. I don't like the shift kit or drilling they did on the 91 sep plate, so who knows what other stuff is done inside.
Good luck