if you go to the old car manuals project site, scroll down to gmc truck manuals and info,down again to 55-59 trucks maintenance manual and click on that. it will open up a new window for you and you will find the info on page 137. there is a figure there that shows how they go together, but basically, from the underside rear mount, there is the bolt head, then a lock washer, then a flat washer, then the rubber bushing and the steel dowel goes in the middle of that. this is all there is below the frame mount. then above the frame mount there is the other rubber part (it doesn't say round or square or whatever, but they are definately square on my 57 gmc 1/2 ton cab) and then the under part of the cab. that site also explains how the front cab mounts as well, but it is basically the same as what i said in the last posting. it is metal on metal with alignment shims or what they call anti squeak shims in between tjhe frame mont and the underside of the cab. it also talks about how to align all the fenders and hood etc in the previous pages. might be worth a look.