Rear cab mounts, slip-on vs OEM

[Brandons63]

Hey guys, just cutting my truck apart, no big deal :P was wondering what's up with the slip-on rear cab mounts? Are the OEM mounts difficult to install? Was ordering some more panels that I'm finding rotted as I go, and found I needed LH and RH kick panels and Rear floor sides. I have the Slip On rear cab mounts that seem much to big, hang below cab about 2" when seated flush with the cab floor. Thanks for the help! (truck is a '63 C10). Pics below are for fun showing this weeks progress. Was just driving it two weeks ago when I decided to ruin it haha