Cool, I had an LC Torana as a paddock basher when I was 16.
There is plenty of usable power to be gained in an aftermarket ecu...PowerFC, Vipec/Link, Haltech etc.
Aftermarket turbos has lots of threads here in Forced Induction with the most commonly spoken about being Hypergear but there are a huge number of options so name a target power figure and that will narrow it down. Click the search button and read.