Yes - it sounds like an interesting car indeed. Having spoken with our Holden History guru; yes - it is most likely that the twin headlight front & sunroof were Holden Dealer fitted options rather than factory fitted options. According to the Guru, Holden heavily promoted the ability & willingness to do special Dealer Optioned up cars back in the 70s. No - no real way of knowing how many Tuxedo Black HJ GTS Monaros were factory built. Would suggest the best history tracking option would be to source where in Aus the car was built, then try to track the Holden Dealer it went to, & then to try & find the Dealer records on same car (yes - may be a very hard route, Dealer tracking wise). Wishing you & your friend all the best with the restoration.