How to track down those few later model parts for your hot rod?

I am having a hell of a time finding the few later model parts that are required for my build. I know traditional cars aren't supposed to use anything newer but I am running a T5 transmission and a later model rear in an otherwise vintage build and I don't think I am the only one. So maybe this is something that can help others?

Anyway, I have figured out all of the channels to find old parts - and with old parts most of the time you are dealing with people who know what the are doing and what they have. What I can't figure out is how to negotiate the world of late model parts. I looked at six Chevy 10 bolt rears (from 91-95 impalas) that were advertised as posi before I gave up and installed my own. I would bring a wrench and pop off the cover to inevitably find an open diff. . . and then have some fool stand there and tell me that an iopen diff was a "posi" . . . the best was a guy who runs a business called "impala king" who couldn't even tell the difference and claimed it was a special clutchless/springless version. Either late model parts guys are all idiots . . .or liars. . . it seems.

Now I need a Chevy pattern WC T-5 with a 26 spline input shaft. I am constantly trying to get sellers to provide tag numbers, photos the counter shaf caps, and count splines so that I can determine if its WC or NWC. . . but all these guys seem to be able to tell me is "what it came out of" which really doesn't mean shit anyway.

How do you guys go about locating the few late model parts you need? Is there some high tech system that I need to negotiate? It there even one person in the world of late model parts whio can do more than repeat like a zombie . ."make? model? year?" but actually knows what he is selling?

 

Sometimes finding a donor car is a good way to go, and drag it to your shop "space". Then trade/sell off the gear you won't use. I found the late model yards have "slightly" inflated idea of the value of used parts. Understatement to follow! (in the East, Car-part.com will list who has what, it's "quality" or condition and usually pricing.)