Yes, I read your last post and unfortunately will have to wait until Monday after work as I'm away from the '68. I will get the measurement from bottom of frame rail to center of the rear axle tube, for you, no problem.
Friday night, I was hawking over Dodge Cummins using AutoTempest ... and today I just bought for $5200, in about Orlando, a '97 Dodge 2500 Club Cab with turbo diesel, 5-speed manual transmission, hydroboost setup, and with a measly 64,000 miles on the odometer. Nothing has been modified to the engine. Truck is just cosmetically ugly. I will get a picture up tomorrow.
I'm going to read up on the governor spring swap and the KDP (killer dowel pin) fix.