I can't speak specifically to the '36 Jimmy but, assuming they are similar if not identical in that era, there should be two bolts through the cross member into the lower core support. You can see them in the pictures below of my 38, just ahead of the balancer on the cross member. The bolts on my 38 were plain old carriage bolts with the heads on the top side. The rubber pad I didn't measure but was a bit less than 1/4" thick if memory serves me correctly.

Hi Stephen

I can't say anything for sure about your GMC either, but '46 Chev trucks had 2 carriage bolts as Tiny describes installed from the top down, through the radiator support, the cushioning pad, the cross member, springs and washers, and nuts.

The cushion was deteriorated and gone on my truck so I can't say what was originally there.

I put in a piece of rubberized belting, but don't remember the thickness.

Probably 1/4 inch, but I can measure if you like.

Interestingly, when I replaced the cushion, the truck became noticeably quieter.  🙂

I will crawl under mine and get picture if I can.

Here is a photo from the front of the radiator support and the other photo is underneath the radiator support.  Can't see the top of the bolts.  The rubber pad is 1/4 inch rubber.  Probably identical to the Chervrolet truck