M101 and M105 are not basically. The same. M101 has a light C channel frame while the M105 has a large box beam frame. Likely weight 3 or 4 times as much. Just one difference. The list is long. Think machine gun vs. tank.
If the axle on the M101 is stock it's probably an 8-lug. As the JK wheels are 5 lug you are unlikely to find a spacer to work. Therefore you will have to replace. A spacer is still needed based on how the spindle on trailer axles are made.
Has any anyone bought the fiberthane material? I have a project that I think it would be well suited for. I found their website (I think) but its very shallow just an order blank really. No product info, company location or even a phone number. Any help would be appreciated.