The kits are available from the vendors who advertise here on the bolt as well as Jim Carter or Classic Parts. Basically you are replacing all the rubber bushings. The rear mounts are a pretty easy job once the mounts are off the truck. The COE mount is similar to these with the exception of the leg going to the body which is COE specific. Reproductions (non-COE) are available for $150+ which unless your set is missing is a bit steep in my opinion. You may also find shims on the frame side or cab side that were originally installed at the factory to a recommended measurement for clearances, they are shown in picture 2.
https://www.flickr.com/photos/advance-design_parts_co/8129483565/in/set-72157631868452754
https://www.flickr.com/photos/advance-design_parts_co/8129510232/in/set-72157631868452754
As to the rear engine mounts you describe the most common type. They do deteriorate over time and can be a bit of a bear to replace due to access for the bolts that attach to the bell housing. There are a couple other types available (NOS only) that were offered as HD alternatives.
https://www.flickr.com/photos/advance-design_parts_co/8461998320/in/set-72157631868452754
https://www.flickr.com/photos/advance-design_parts_co/8461998216/in/set-72157631868452754

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr