You need 3M 20mm wide double-sided tape to fit to the helmet. The curve on the inside is profiled to the helmet (see images).

Yes

Yes

.12

20%

I initially printed this with the base side on the bed - however to enable 3M double sided mounting tape to fix strongly, I had to sand it down to a 2000 grit. It is probably better to print it on its side so this is not an issue.I used the bolt and screw from the broken mount.