Found this info from a Google search. Note that the Controlled Differential is NOT a traditional friction-type posi unit.
From what I have gathered in classic Cadillac forums this is the original control diff fluid part number.
Part Number 1050189
Then Part Number was superseded by part number 1050081.
http://www.gmpartswiki.com/getpage?pageid=128705
Then part number 1050081 was superseded by part number 1052271.
http://www.gmpartswiki.com/getpage?pageid=93213
Then the trail leads to 89021671 - 80/90W Rear Axle Lubricant Supersedes: GM# 1052271
http://www.amazon.com/Genuine-Fluid-89021671-80W-90-Lubricant/dp/B00BK7LUTM
The big pre-formed brake line companies will typically give you the first one for free if you provide a pattern for a product that they don't currently make. I suspect what happened here is that the company sent out a "form letter" response to every name on the waiting list. Have you contacted the person that you worked with originally?
All the vacuum diagrams are in the factory Chassis Service Manual. 2bbl or 4bbl? With or without A/C, with or without other vacuum operated options like trunk release, etc, will all matter.
Just bought another. 1969 Cutlass flattop wagon, 44K original miles. 350 2bbl, three-on-the-tree, power disc brakes, manual steering, no A/C. NV car via Phoenix. Hopefully it will be delivered by the end of this week.
Depending on certain combinations of rear gears and tire diameter, it isn't always possible to hit the correct ratio using only the drive and driven gears in the trans. Keep in mind that the gears have discrete numbers of teeth, so the ratios you can get are not infinitely variable.
These ratio adapters were typically installed right at the transmission, not mid-cable. In this case, however, they were factory installed on the 78-79 Trans Ams with the Borg Warner Super T10 four speed.
Post a photo of the servo. As others have pointed out, GM only used a two-piece speedo cable on cars with cruise. There were also aftermarket cruise control units and also speed sensors for early trip computers. Hard to tell without seeing what we're talking about.