After 1998 here is what's available...
Reg cab / Long bed
Ext Cab / Long Bed
Ext Cab / Short Bed
Quad Cab / Short Bed
Quad Cab Long Bed
There was never a 3/4 ton+ made in a short bed, reg. cab.
Although some Reg. Cab long Beds do look like reg cab short beds.
It's going to cost about $3,000 for a good job. But,, the truck will look freakin' brand new especially if you clean up the carpet alot, and re-upholster the seats.
Merrick