Here you can see the referenced measurement from the FAM, and yes 3/4" is probably close enough. I have parted several trucks that have included shims, sometimes on the frame but most often on the cab.
https://www.flickr.com/photos/advance-design_parts_co/14779252972/in/album-72157631868452754/
Here are a couple pictures of the shims referenced above.
https://www.flickr.com/photos/advance-design_parts_co/14595267579/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/8129510232/in/album-72157631868452754/
There are no cushion pads on the rear, only on the front mount do you find pads. The early center mount used a bumper on each side because the cab flexed, the later internally cushioned shackles eliminated the need for them.
https://www.flickr.com/photos/advance-design_parts_co/8129470535/in/album-72157631868452754/