Advance Adapters hasn't fallen 'short' on this one - a new shorty GM SM465 to Jeep Dana 18/20 adapter kit.  At 7/8” length, their adapter kit is the shortest on the market, providing a combined transmission-and-adapter length of only 12-7/8”.

They didn’t stop there.  

Their adapter is manufacture from a Blanchard ground steel plate and features three transfer case clocking options.  These clocking options are 20, 33, and 40 degree intervals.  The clocking options will allow a fine-tune conversion to maximize clearance between the transmission and yoke. 

To obtain the adapter length of 7/8” they had to manufacture a new SM465 main shaft.  This new main shaft fits 6 spline drive gears only.