Pick up the phone & give Sureflo Exhaust a call (02 98293158) & ask them to compare the HSV Headers to their 1" 7/8 4-1's.
But as per usual, you probably know better.
Do this for headers/cats only.
There catback is the biggest P.O.S on the market, i bought one and fitted it, went to get a tune etc and my mechanic/tuner told me it needed around about $600 to straighten it and fix it up[in less than 250km it had shifted and was hitting on the trans tunnel and was fkn wack at the rear end]. Rang sureflo explained to them what had happened and what it'd cost to fix, i sent them pics and email and they wanted me to send it to them at my cost.Bit the bullet and replaced it, now i tell people not to touch there catback exhausts. Biggest bunch of jokers going around, and for the money they charge for a catback there is better stuff out there for less.