Nick,
Be a little bit wary when you add seatbelts... some NSW Inspection Stations require fully compliance to ADR5 for any added seatbelt (even in early Holdens that otherwise don't need to comply to ADRs). ADR5 has some fiddly requirements regarding the minimum separation of the belt bolts (... dont ask me how I know
). Might pay to double check with your Inspection Station/engineer before getting the drill out.
This post has some good info:
http://www.fbekholden.com/forum/viewtopic.php?f=29&t=13825Cheers,
Harv (chief apprentice seatbelt fiddler).