From what I remember, all chassis use the same engine and trans mounts, but, the toe link mount on the 84-87 overhangs the rear trans mount, on an 88, this overhang isn't there. That overhang also prevents Thelin's rear transmission mount from fitting an 84-87 without cutting the car, or the mount. Personally, I would hold out for an 88 cradle and know that everything is exactly like it should be.
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."