Sounds about right you're up for about 3-$400 in hub adaptors.
I've used the eBay ones previously from seller Mywayadaptor they were pretty good quality and machined perfectly to specs I had ordered.
Which model commodore wheels are you thinking of using as they might not look great on a 240 unless you're planning to run the steel wheels?
What size tyres are on the wheels currently?
This website is an excellent resource for calculating changes in wheel/tyre size
https://www.willtheyfit.com/