the 39-48 trucks are tiny inside indeed. but the 33-35's are smaller still. then i chopped and channeled my humpback to boot. and set the engine back. and added a cage. but the seat position will be set back over a foot, so i at least have some leg room. and at almost 6' tall with age and health issues, i can't bend very good any more. BUT i'm RESOLVED to try to finish this dadgummed thing somehow before i cash in if it's possible ! the crew cab truck you show has has considerable fab work done, and anything is possible with the right talent and equipment. but if you don't posses much of either,[and PLEASE don't take this as in any way a slam on you or your talents !] i can see a project going down hill fast. with that being said, what about a 38-39 coupe with the tail cut off behind the 1/4 windows and a rear "cab" panel fabbed. then add a box. then chose what ever year dak chassis that would fit your wheelbase needs. this MAY be easier to fab into your club cab vision, as you could move the seat back into the 1/4 window area for leg room. this probably isn't being conveyed very well, so you may need to use your imagination to see what is in my mind. this may be easier to pull off than joining 2 cab sections, or fabbing sections needed to accomplish your vision. a suggestion you may consider is this. take several side view pics of coupes that may interest you. then use scissors and cut the rear portion off some where just before the trunk lid opening. add a pickup bed from another pic and see what that looks like. it may look good, may not. or, if you are just a little more "puter" savvy than me[which wouldn't take much !] you could do this in a program like "paint" maybe? just throwing out some ideas. you may find these useful, or you may decide i'm just a blubbering old man. my feelings wouldn't be hurt in the least. just trying to help you decide on a project that could be completed rather than started, then tossed aside because of whatever reason and never finished. there are way too many of those around. i personally think you have a great idea to express your creativity.
beer