Just a couple thoughts on this. I would sugest conferming the fit of the adaptor to the hub. Use a sharpy to mark up the inside of the adaptor and then fit each half to the hub and rotate it back and forth, inspect the inside of the adaptor for contact to the hub. If it is a good fit the ink should be scuffed fairly evenly. If the adaptor is too big you will see one contact point in the center of the radius, if it is too small the outside edges will show contact.
That being said and assuming you have aprox. 80% contact or better, you might consider some double sided tape. (We actually have machined parts with this stuff). If you have a good fit and tighten the adaptor over the tape I dont think it is going to slip, I reckon you end up with six square inches of purchase, traction, or grip.
It sonds like some locktight could be used on the bolts. Get your chain alignment set up, then locktight one bolt at a time.
Discalimer: These are just common sense assesments not based on an actual application. Hope it might help.