After some testing last night one thing has become readily apparent:-
The Corolla & the NSU mods are clearly head and shoulders above the Fulvia & R8 mods. While they (NSU & Toyota) have their own small quirks to mark individuality, they feel like a GTL car, similar to the way the Ferrari 250 & Porsche 904 feel.
The Fulvia & R8 both feel pretty sketchy and both have some really unusual handling quirks that just didn't do it for me, tbh. They actually made me less confident the more laps I drove.
I'm erring on the side of moving them out of this event and changing the format round.
I'd be inclined to have a 3 race event where you have to drive both the mod cars and a default car, but the order you drive them is up to you, but I'll leave a few other options in there for you.
I'll put up a poll so you can decide.