haha... I have to admit a bit of ignorance here...

I just checked today (before reading the posts) and noticed exactly what you were so astute to point out, that the GM compressors use a 6-serp and the dodge/cummins an 8-serp.... That makes a direct retrofit an unlikely option, since playing with pulleys on an A/C compressor is a dicey situation, IMHO. Hopefully nothing a trip to the junkyard won't fix (for an 8-serp compressor).
When i put the GM hydro-boost on my truck, I used the pulley that came with the 6.2 diesel pump which was out of allignment with my 4.3L V6 pulleys by no more than 1/4", subsequently shredding my serp belt in under 10 seconds... So i'm leery to start experimenting with differing pulley configs... Guess my easy fix is out... Shame is i just topped up my system with some R12a... Oh well...
As far as bracketing goes, I've got a 'clean slate' for development of a bracket... (within the limitations of the belt tensioner and drive pulleys, of course...) I've run across the factory brackets (in other forums/posts) and am trying to construct a CAD file for the profile to make it easier for future conversions. The basis for my design is the 2-piece standoff (A/C & coolant-intake/idler/alternator) vs. the all-in-one plate that is found on the 12-v 5.9 cummins (1992ish) that come up on e-bay. Unless someone happens to know the P/N for the bracket i'm talking about, and it's reasonably priced, I'd rather invest my time and gain a little experience doin' it myself.
Also, machining parts is expensive, so if there's a way to have a 'rough cut' a 1/4"-3/8" steel plate with some feet/spacers, i would imagine that's a much more viable (read cheap) option for other 4BT conversions.
Our heli-mechanic's 5.9 dodge has been sitting in the parking lot for the past week, so i've been taking measurements of the 'factory' brackets for a baseline... With the comments i've read here, it sounds like i might be better off putting the motor in first, and then making brackets to fit equipment after... I don't like the idea of cutting the frame too much, even though it looks inevitable with the starter motor, but who knows... if anyone knows, let me know!
Has anyone experimented with different water-pump coolant intake diameters? The factory one is over 2", I want to be able to weld a nipple onto my new plate, but the largest i can find at a big-box store (Dome Hepot, wink wink) is a 1-1/4" fitting... will this flow enough coolant?
As for the full-sized K2500 IFS and 14-bolt 9.5" upgrades, those are 'phase 2' upgrades, but I will definitely post updates as to progress on those. My inspiration for the front-end upgrade came from a 6" suspension lift-kit for the S-10 that dropped the IFS and front control arms for what I was hoping was going to be a GM 6.2L conversion for my A/C equipped S-10.... (the 6.2 has been relegated to my non-A/C '84 jimmy) So i figured, with the under-vs-over spring slung axles (9.5 vs 7.5, respectively) instead of just dropping the puny front suspension (IMHO) with bolt-in brackets, I may as well use something from a heavy-duty full-size pickup, hopefully solving the lift and potential wheelbase increase required to keep the handling the same as before (with a few hundred extra pounds from the motor), but with adding a few more inches of clearance, and the capacity for a few more ponies.....
Something else I mentioned in a previous post that i've taken a good look at now is the 700R4 TV setup.... I realized that the throttle/cruise control work in a 'retraction' manner, while the TV cable works in an 'extention' manner..... That is to say (for people unfarmiliar with the system), as the go-pedal is depressed, the throttle cable retratcts, pulling the throttle 'arm' towards the firewall.... At the same time, the 700R4's TV (throttle valve) cable needs to extend the cable away from the firewall... Now, the TV cable IS adjustable, but from what i've observed, there is a minimum ammount of travel required, otherwise you risk burning clutches and all sorts of shift problems... (I'm planning on measuring the TV travel on my 4.3 to establish a baseline.) I may see a solution in a custom bracket attached to the opposite side of the VP44 throttle-arm, but it looks like I only have just over an inch of TV cable travel.... (I've smoked a 700R4 with improper settings right after a rebuild, so I'm leery about just allowing for an arbitrary ammount of TV travel....) I may end up building a 4L60E/4L80E transmission controller yet... I hate the thought of buying an 'off-the-shelf' unit for nearly a thousand bucks when I can build a 'custom' ECM/PCM/whatever-they-call-em-these-days for a fraction of the cost.
Oh, since the rear-axle is a phase-2 project (post 4BT) i'm thinking of fabricating the brackets to do a drum-brake conversion. If that is the case, I'll probably upload the CAD files to save others a butt-load of work
Once again, always apreciate advice/input, and thanks.... (i'm all 'outa smilies)