I once found a 1973 D150 Adventurer 2wd with a for sale sign on the side of the road. Popped the hood to find a 400 2bbl. Guy wanted $350 IIRC, so I went back to pick it up. Drove it home. On the way home I realized it had the factory Tach in the dash. Didn't even cross my mind to look , but hanging underneath was an 8 3/4 diff. Checked the gears and low and behold 3:55's and Suregrip!! Turned out to be a sweet score!