I 'think' it started in 74? I got a set of 8 3/4 truck axles from @Righty Tighty a few years ago. They have the big-big bolt pattern like a Ford truck or a Jeep. They are the exact same length as the axles in the 8 3/4 truck rearend I bought at the N. GA Swap meet, but those axles have standard 4.5 bolt pattern. I'm almost positive that my cousin's old 74 Power Wagon that we used to beat around the woods in had the 5.5 bolt pattern also.
