I was having a think about this and a few things you mentioned earlier.
Just going to list some thoughts, you probably already have considered and chosen a path, but not mentioned...
1. Rear-end. You mentioned aframe boge removal / polyair springs etc. Does your RRC have swaybars?
Some thoughts around this are:
remove bars, keep boge, new balljoint, clean upper balljoint. forget polyairs unless you're going to randomly cart heavy loads or the load won't be 'constant'
by that I mean, you'd be better off with a set of springs more-suited to your application as well as dampers to match.
Ditching the swaybar for the additional articulation - but also again requires spring & damper modifications if you want to get the most out of your suspension - alternatively, you can use a swaybar disconnect - a cheap pin style or the super-duper locking hub style that LRA make for exhorbitant fees.
2. propshafts - I know you said you were looking for non-donut version, and that you currently don't have propshafts that you could use / modify.
It may be worth your while having a couple sent over from the USA from Tom Woods - at least then you know exactly what you will get for your $$$ is top shelf and pretty much unbrakeable. (Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist)
I've had local engineering firms make propshafts for me in the past as well as rebuilding and customizing MB ones (which have non-replaceable centre uni's) and Tom's prices for a brand new shaft are cheaper. Hate to say it... but worth thinking about.
3. R380 - is not a bad box, but it's not without it's known issues. Perhaps it is worthwhile rebuilding and performing necessary upgrades to make it a bulletproof unit? Same as the LT230 - they are good for what they are and pretty reliable, but can still do with quite a few improvements to make them 'bulletproof' - more time consuming than financial... stuff like double-row bearing mod on the rear output, crossdrilled gear, maybe an ashcroft atb centre if you have some flash money or something.... I'm just throwing ideas out there - you have the stuff already and don't have to remove it from the vehicle, so you're already more than one step ahead.
Like I said, you probably have already thought this stuff through and have a plan, but it would be interesting to know if you've decided what path you're thinking of taking on the suspension side of things, because the use case for the vehicle is a very specific guideline for suspension choice and modifications(if any).
Interested to know your thoughts. Got any more pics of the shell?

