Tim said "Is there a short enclosed-u-joint housing/extension on some Chevrolet 3/4 tons or GMC longbed 1/2 tons that are then connected to an open driveshaft?"
Yes, my 51 3600 with it's SM420 had a enclosed driveshaft to the carrier bearing. From the carrier bearing to the rearend it was a typical open driveshaft.
Now, I'm totally out of my area of 1st hand knowledge but could one not duplicate the 3600 style enclosed/open driveshaft with the three speed which is what I believe tclederman was saying? A bit of measuring, cutting, fabbing/welding up the driveshafts and cross member for the new carrier bearing and one's in business, a nice weekend project.
Good luck, RonR
