The 137" wheelbase still has a two piece driveshaft, the rear shaft is same (or close), front gets shorter.
Shortening the frame is a lot of work, and usually detracts from the value of the vehicle, even if done really well. I know in my past hunts for old trucks I quickly passed by trucks with modified frames, unless perfect otherwise I suppose.
If there's any reasonable way you can keep the truck much like it is I think you'll be better off all around.
