If you can find a farm truck that has spent most of its life in a shed you might well be able to sell the cab for what you paid for the whole truck and have a lot of parts left over. 100 series GMC through 500 series used the same cab. A solid cab to begin with is the best way to restore. There have been lots of guys that put patch panels ever where on a rust bucket and never completed the project. They either ran out of money or lost interest.