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?

Thanks.

Joe
--
Heather & Joe Way
Sierra Specialty Automotive
Brake cylinders sleeved with brass
Gus Wilson Stories
http://www.brakecylinder.com