http://dieselplace.com/forum/showthread.php?t=32125&highlight=folding+rear+seat

Can an extended cab truck have a 60/40 folding rear seat?

Do you mean a fullsized 60/40 from a crew cab? Without having actual measurements I would have to guess it would not fit. If it did I don't think there'd be any space between the seats base and the back of the front seats. You'd probably also have to move the front seats forward a bit as well. As far as th eaftermarket offering a 60/40 extended cab seat option I've never seen one. Probably out there though.