Yes it is the rear one. 1-3/4 approx and front is over 2".
The norvil style top iso will slightly support some additional weight & thrust.
separate:
The thing I have learned is that, when the bike is left on the side stand for a long time, the lower iso's take a set.
The set in the rubbers makes the engine/tranny/cradle sit a bit crooked (to the side) from it's original position.
This was discovered at a removal of the headsteady and found the engine tilted a bit and the engine had to be stressed to get the 3 head steady holes to line up on top of the head.
Further, this side load made the chassis vibrate more due to the side thrust through the top iso washers.
therefore:
The side thrust vibrations would therefore also happen in a link type mount.
When first installed 1988? the norvil was 100% ok by me.