Welcome to the forum mate, I also drive a 40th anniversary but in midnight purple. Your best to search the forums and do some reading on the first mods to do and just rock up to any cruises/meets/dinners in your area.
When we did our Project car we worked out the factory speakers are actually 6-3/4" (oversize) which are 17cm speakers. Pioneer make a direct replacement if you don't want to stuff around with chopping and grinding and re-use the standard black insert and speaker grille.
I can supply you with Earls fitting (709108) for $32 each if your interested.
Basically we can give you 30% off the list price of ALL Earls Fittings and Hoses.
No it doesn't shatter and turn into little tiny javelins. Having broken carbon items myself I can tell you that this really is a myth.
Also helmets come under the Australian Standard (AS/NZS1698) not ADR.