Third Member Swap Issue

Got a really clean 3rd member off Craigslist with 3.73s to swap into my '13 5-lug. Everything looked like it checked out. Buddy and I visually checked bolt holes, ring and pinion spline count to make sure it was the correct 3.727 ratio (41 ring : 11 pinion). Looked good so we pulled mine, got the new one sealed up and torqued down, however when it came to bolting up the driveshaft, we found the flange bolt pattern was off...

I am suspecting the previous owner removed this carrier from his 2010 4x4, and before selling it to me tried to bolt it up to a 1st gen or something. The flange on it had a bolt pattern that was 1/4" too small for my driveshaft (2 3/8" side-to-side vs my 2 5/8" or diagonally 3 1/4" vs 3 3/4"). It looked like at some point he pulled his flange off (which even with a 3 ft breaker bar, we could not) and replaced it with a smaller size thinking it could fit another truck. He didnt tell me this, and I stupidly didnt measure. So since we couldnt take that flange off, my truck is sitting with a gaping hole where the diff should be, and I have two third members sitting in the garage. I'll be contacting a offroad or machine shop this week to see if someone can swap my flange onto this new one.

If anyone has knowledge on this aspect of third members, feel free to chime in. If you know any 1st Gen guys and gals or if you know the driveshaft bolt patterns of 1st Gens, post up if it's close to what I found. Would be nice to know this isnt a case of certain 2nd Gen 4x4's having different drive shaft sizes/patterns.

Mods, if this is the wrong forum (or there's a better one) feel free to move it. Thank you.