I have heard from various sources that the meteor breech jaws are hollow, so suggest not drilling them.

No reason however not to have a nice round head bolt/nut in place of the pin though; won't look quite as neat, but then you won't wreck the gun

post 22 on this thread:
http://www.airgunbbs.com/showthread....wer-BSA-meteor

(have heard this elsewhere too, and in other articles about their construction)