CX/GL650 axles are larger than the ones the 500s have. I'm not sure offhand whether the 1100s are bigger than those but yeah, they would be bigger than the 500s have.
That wouldn't be a consideration for me because I'd probably want to replace the bearings anyway so replacing the spacer between them to fit the 500 axle shouldn't be a huge deal. That's what I did when I used Honda wheels on the sidecars - they have stub axles so they need to be pretty big...
The 650 axle is smaller than the 1100. Even if the right bearings can be found to mate the wheel and axle, the brake caliper will stinn need to be sleeved.
The dust shield on the final drive conflicts with the wheel hub, as well. It seems the usual solution there is to mill down the flange on the wheel.
I believe you about the axle, I just have never had them next to each other to compare (my CX has a 500 axle and I never have wheels off of both bikes at the same time).
I haven't directly compared them but the CX500 final drive on Eccles and the GL1100 one on the 'Wing look identical except for the dust shields (the 1100 is even 3 stud). The dust shields are only held on by 2 screws so it should be easy to put an 1100 shield on a CX FD.
Anyway, I think we can agree that it is possible but it isn't anywhere near as easy as switching to an 18" CX500 wheel...
I bought a GL1100 final drive to try its dust shield on the 500 unit. The case behind the shield is different enough that it wouldn't be a simple substitution. I think it wouldn't even be adaptable, but haven't made a concerted effort yet.
My current direction is to use Comstars and adapt the CX front to the donor forks. I'm sure I'll go back and forth a few times before I get to the end.