question is can this shaft be shortened to work?
The topic of this type of propeller shaft came up on For C-Bodies Only (FCBO). I provided an information post there that I will also post here in the following.
Regarding the question of shortening, It's not advisable for this type of shaft, especially with its age and possible isolation condition. If attempted, it likely should be done at the front end. The back end with the outer and inner tubes coupled with the internal rubber isolation rings complicate any shortening, although it might be bypassed by removing the inner shaft and isolation and using just the outer tube and different universal joint yoke.
Borrowing a picture from the FCBO query, shows part of the rubber isolating rings failing in a 1968 propeller shaft:
Following is the posting I made on FCBO, FYI....
Chrysler introduced the Internal Vibration Absorber (IVA) propeller shaft (aka drive shaft) for certain applications for the 1966 model year. Applications were determined through Noise/Vibration/Harshness (NVH) studies. Two approaches include the addition of the inertia ring at the front of the shaft, or a rubber isolation with inner and outer shells added at the rear of the shaft. These approaches were phased out in later years as other NVH control methods were used in body structure, suspension mounting, etc. 1966 was also when the constant velocity joints were dropped in favor of cross and roller universal joints on all models except Imperial.
From:
Additional industry-wide information for the IVA Propeller Shaft can be found in SAE technical paper, " Axle Noise Control - The IVA Propeller Shaft", Product Code 690259, Jan 31, 1969.
