Welcome to the forum Preston
Congratulations on the new truck project. About 90% of the time I recommend keeping the frame that is original to the truck or at least the same style of frame. For one there are possible legal issues with a frame swap. With the '73-'87 frame, you will have to fabricate all of the body to frame mounts and you will end up with about a 3" body lift. It is really not something for a beginner fabricator. The only way around that is to do some channeling of the cab and bed floor.