In 1966, the HO 52 is shown as a 4.11 or 4.57 on page 13 of the axles section, and it appears that in 1969, at least according to the GM heritage docs, that the Eaton was referred to as a 4.10 in the 3/4 ton trucks. I would like to state for the record, that I was never debating the semantics of 4.10 vs. 4.11. I was weighing in because the information the OP needed was what his options for finding higher gears are.
https://www.gmheritagecenter.com/do...hevrolet-Trucks/1966-Chevrolet-Truck.pdfhttps://www.gmheritagecenter.com/do...hevrolet-Trucks/1969-Chevrolet-Truck.pdf
