I was thinking more about the chassis's ability to handle that sort of hp! :-) Reliably anyway. Plus stuff like unis, leaf springs, brakes etc!

I know little about Gilmer drives though, so can't really help on that front. Maybe look at what the carbied group C and group A cars were running, they were pulling 450hp or thereabouts. There are a few of them around still running as per original engine bays. Most of the A9X's that finished in the top 5 or so from 1979 are still kicking around, and a lot of the VC-VL Commodores are still around too. What sort of 308 is it that develops 500+ hp? I assume it is blown? Or at least stroked to near 400ci?