G'day NES,
Just a thought before you start drilling - have you checked with your rego authority (or engineer) on how anal retentive they want to be on seatbelts? If the car is getting engineered, it's up to the individual engineer. If you are going normal NSW rego, then it will be assessed by an RTA Authorised Restraint Fitting Station (
http://www.rta.nsw.gov.au/cgi-bin/index.cgi?action=authrestraintfitting.form). This is not an engineers certificate, just an inspection and basic form to sign off and fairly cheap (>$100). Most fitting Stations will not let you do the work yourself (to a decent standard) and then inspect and certify it - most will only certify if they do the work themselves (in the end it's their signature on the line).
Some Fitting Stations (and engineers) require full compliance to ADR5 (
http://www.comlaw.gov.au/Details/F2009C00157/Html/Text#_Toc1235628295870) when you install - there are some tricky bits in ADR/5 about how far apart the belts can be that will determine where you start drilling. I got caught out, and had to redrill some holes in my C pillars... not fun. You nearly need to be a rocket scientist to decipher ADR5. I've started a simple laymans explanation (with pictures
) but havn't got round to finishing it yet.
Engineers often reference the National Code of Practice for Light Vehicle Construction and Modification Section LK Seating and Occupant Protection (often referred to as NCOP). NCOP is virtually identical to the requirements of ADR4 and ADR5 for seatbelt mounts... just not structured as well in it's text.
Cheers,
Harv