[roger0080]

FWIW, I am looking at 2 manuals here. Both list that you could get a Dana 60 in a half-ton.

Manual #1 is manual number XR60-GM, "Model-60 GMC/Chevrolet 1967-1978, Spicer Axles/Rear" by the Dana Corporation.
This lists all the Bill of Material Numbers, part numbers etc. etc.
It lists that the Dana 60 was installed/available on C-10's in the years of 1968,1969,1970 and on K-10's in the year 1967.

Manual #2 is manual number X-172001 GMC Trucks Master Parts Book Models 1500,2500,3500 (for 1972).
In the Model line up, it lists a "Spicer SS 60-35" as an optional rear axle for certain models 67-70 (but doesn't list it for the 67 K10 as the Dana manual does).

From the 72 GMC parts manual, it looks like the Dana 60-35 is a six bolt axle flange where as a regular Dana 60 is an eight bolt axle flange.

So, if you had a Dana 60 in a half-ton in 1967-1970, I don't know what they called it, technically, and agree that the "heavy half" nomenclature is carry over from they 1973+ years.

Confusion abounds in that when people say "heavy half" they may not be referring about the "leagality" of the name but what it represents -- a half ton with a three-quarter ton axle/running gear under it. Did or did not GM ship out the door a half-ton with a three-quarter ton rear in it?

According the manuals and peoples recollections (including mine, but I thought I saw 8 bolt hubs on the few I've "seen"), I think they did. I am not a Dana expert so I can't tell you exactly what a Dana 60-35 is other than it is a Dana 60 of some sort.

Just my 2 cents and I may be wrong on my "recollections".