3/4 Ton GM Third Member Swaps

I've been all over Stovebolt.com, and over to chevytrucks.org, and elsewhere, trying to verify information about swapping 1967-1972 GM
3/4 ton third members into earlier 3/4 ton rear ends.
My understanding is that the '67-'72 pumpkin can be swapped into 3/4 ton rears from the late '30s up through Task Force trucks. I can find a number of posts that seem to confirm this for Advance Design ('47-'54) trucks, but none for TF. I have access to a '52 3/4 ton rear for inspection purposes, and the pumpkin appears identical in every respect I can see to the one in the 1959 rear my friend wants to change.
I found one post that seems to say the AD and earlier axles are 17 spline while the TF and '67-'72 axles are 30 spline, so if you're swapping into an AD or earlier rear you need to get the later axles and shorten them about 1/2".
But I can't find any posts where the poster flat out states that he did this swap into a TF 3/4 ton rear end, with a '67-'72 pumpkin, and it worked.
My friend has talked to a couple of differential "experts" and a couple of truck wrecking yards, and they all say they've never heard of this swap for any of the older trucks. I know I've read about this many times here and on the OleTrucks mailing list, so I think these "experts" are wrong, but I would like to get some confirmation before I advise my friend to spend $400-$500 for a later third member.
Who's been there and done that?
Heather & Joe Way
Sierra Specialty Automotive
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