I am pretty darned sure the cabs cross over.  Not sure about the extra cab to single cab thing. Depends on the back cab mounts/front most bed mounts lining up.  Sure wouldn't be tough to relocate some mounts though.  Whenever we had body swapped, which has been 1st gen 4runner to 3rd gen pickup frame and a 3rd gen extra cab to a 1st gen long bed pickup frame, the front mounts pretty much line up, the rear cab mounts by the back of your seat usually nearly line up.  A little fabrication and massaging has always been involved swapping generations of bodies and frames but it's not really tough.

Basically what I am trying to say is if you are swapping the same body style I don't think you will have much to do, if anything.