For GM T350, 400 & 700R4 and many others.
Upper holes are for 7/16″ bolts and are slotted for 3-1/2″ – 4-1/2″ centers. The lower holes are 7/16-14 on 1-1/2″ centers. The insulator is 1-7/8″ tall.
We now stock the Energy Suspension polyurethane mount. It is stiffer than the rubber insulator, and will hold the transmission more securely than the rubber mount. I used rubber engine and transmission mounts on the '32 when I built it. After switching to urethane engine and transmission mounts at 35,000 miles, I highly prefer the urethane. They greatly reduced engine rocking on startup and acceleration; this helped keep the car from "jiggling" at idle.