First off, wow - sorry. How many miles was the ploding at?
The 241OR 4:1 and the NV3550 4:1 1st is amazing to slow crawl in and idle over crap - but it's slowwwwwww in most every gear, tops at 15-20 in 5th which feels to dangerous to me to drive at. So I either bog in 4H depending on 1st 4:1 or have to go slow in 4L. Maybe if I wasn't -10% under stock speed at the axles, 4L wouldn't be as bad.
My only other experience was with the stock setup on my 95YJ and AX5 with NP231 and +12% over stock speed from the 31" BFG KM2s. The 4L made it adequate in the dirt and climbing, but still had no crawling ability, but could maintain speed easier.
Tom Woods may be a point of contact for advice too. I've heard their name a few times and my Rubi came with one after the prev owner twisted up the stock one.
My own opinion would be set a course for the finished product. If you want to do the disel or hemi swap you had mentioned, plan that out and find another NP231 to rebuild or just chuck under your ride or park it and complete the swap now. I know I'd get stuck on these milestones and spend double to do it over, and over, and over like my shocks until I finally got the ones I had wanted to begin with, which in turn wasted time and money. I'd probably get it back running on the cheap then map out my dream and make the action plan. I'll shut up know before Jeffy charges me by the letter.