I think you have a pretty good plan. Better than mine actually. I was in kind of the same situation, and my cab and doghouse are in very bad condition. So I though wth, I'll do a swb frame swap, make my frame really nice and drive the body the way that it is. Well, while removing the doghouse to steal some parts from the lwb frame that my cab is still on what little sheet metal that was holding it all together literally fell apart. So, I guess it is really up to how bad the cab really is as to whether or not it is wise to go ahead and dismantle it when your not ready to replace some cancerous steel.
