Never heard of /6s being separated by "gens". Is this the engine from your 85 d100?
That is rather late for the /6 engine though the "how to" is pretty much the same thru the whole run. Or are you referring to the "gen" of that truck?
Something else I never understood. Dodge has made trucks for 63 years before your 1985. I never understood the meaning behind that version being "1st gen" as that would imply that these were the 1st trucks dodge ever created.
What makes you think you need a rebuild? I have a /6 here on a stand that happens to have come out of my own 85 d150 and ran like a swiss watch when removed. Just shy of 100k. I only pulled it because I built another /6 with hopefully "more power" (think.... Tim Taylor on the TV show "home improvement") to replace it.
I'm sure there are others but in that general area of the US, if I needed help I think I'd look up one of 2 or 3 people for guidance .. our own "Dart 270" (north Carolina) maybe Rob Simmons (TN I think) or another guy, mostly on FABO as "Rusty Rat Rod" occasionally on here as "Stroker Scamp" he's out of Macon GA area. Any of these guys could guide you well, as to whether they'd have time or space to build an engine for someone else, I'd have to leave that up to them. Or stay tuned here on the forum, search old posts, and do it yourself, we can all answer questions that may come up.
I'm sure there are other /6 people in the broad area you mentioned, these are just the first that come to mind. All of these are individuals, not "shops". It takes people with a special interest in them, like all of us here on this forum, to be interested in a project like you are asking about.
I am not surprised you are having difficulty finding a regular "shop" to work on such an "old" truck. It's carbureted, has no "ECM" that can be "scanned for codes" so many younger guys would be lost on such a project.

I have had a few Slant 6 engines (maybe 4?) rebuilt by Terry Walters Engines in Roanoke, VA. Excellent work and fair (not cheap) prices. Yes, good engine shops are getting harder to find.

Lou

I can personally recommend Doug’s book. I got a copy during my rebuild nearly four years ago. Using that and input from folks on this message board I was able to complete my first slant six build with confidence. And if you haven’t done so already, check out The Best of Doctor Dodge on the Engine FAQ page.
http://www.slantsix.org/forum/viewtopic.php?t=41326
Good luck with your build.

What year is the engine? Not sure about '80s cast crank blocks, but anything earlier than 1980 can likely go 0.100 over. Why do you think it needs to be bored? Does it have substantial ring ridges? You might just hone and put in new rings and bearings.

Lou

Located where? Slants are still pretty readily available, might be better to start fresh with another.
I know where there's one at, and it's even out of an 85 truck. All stock, running engine.