Regarding the mounting screws you can file the side of the motors to make a flat face and have some clearance for the hex bolt heads.
There's a couple of things you can look at for your PE, frequency spikes and tracking noise.
I'll assume that your mount is new enough that the RA disc is square with the RA shaft and when your clutch is engaged the pressure is evenly spread over the surface.
The ideal vertical worm meshing will depend on how high/low is your spur gear. So with your clutch locked (not over tightened that you "smash" your thrust bearings) push the worm block in the gear to mate it and see if there's a thin gap under it. If there is shim it with some alu shim (coke can or other if thinner).
Once you have that sorted out engaged it completely in the spur gear then release the pressure as you encounter "hard spots".
If you have a smooth motion during your PE run then you're good. If it's noisy randomly you might have to thick a grease in your thrust bearings or the worm/gear grease is sticky too. So check that as well.
If your PE is smooth but still too big check your couplings and the centering of the motor pinion in your gearbox. With the single worm block it is very hard to misalign the worm bearings anymore but try to keep the couplers inline as much as possible. That should turn by hand really easy with no pressure at all. If your G11 sounds like a coffee grinder then recenter the motor pinion in the gearbox until it stops then secure the motor. When everything sounds good and quieter run your PE again.
