Ah, that's very interesting...I've rebuilt D35s and found them unlike the AMC Model 20, maybe the 15 does not follow the design features of the Model 20? A quick way to determine this might be a ring-and-pinion or carrier comparison or parts interchange search. I do not have a schematic drawing of the AMC Model 15 axle, only the 20.
See if you can find an AMC Model 15 parts illustration, perhaps from an AMC factory workshop manual. Do you have the Eagle OE shop manual? Copy a parts or service illustration to a .jpg and share, please.
This is intriguing, indeed. I'm always interested in new findings, and this is news to me. One thing you mentioned is the 7.5" ring gear. The D35 is slightly larger, though that may be a technicality and not significant. The concerns are carrier design, ring gear bolt pattern and diameter, the shim and housing bore locations, bearing sizes (another way to cross reference, incidentally*), the axle shaft splines and count, and the depth/length and diameter of the pinion shaft. A ring-and-pinion aftermarket gear source may be able to cross reference the AMC 15 versus the D35.
Note: For a quick parts interchange approach, head down to your local NAPA store or bearing supply and have them look up the differential carrier and pinion bearings for both the AMC 15 and the D35. See what's really going on here. This is a quick and simple way to determine bearing and shaft sizes, carrier bearing saddle O.D. and so forth—essentially "reverse engineering".
Finding a 2.73, 3.08 or 3.54 front axle from an Eagle would be sensible if not too costly or hard to find. That brings into account more popular D35 rear axle options, especially the 3.08 and 3.55 (which works with a Dana 30 3.54 front).
AMC 20 axles have a distinctly different bearing and shim layout than any Dana axle...Let's dig deeper, Rich!
P.S.: Thanks for your comments on my Jeep Owner's Bible, Rich, had a feeling you knew the "Jeep Thing", too!