A lot of the actual cars and liveries were playable in GT2. Virtue of almost any car having a race modified version or two.
Race '07 with DLC on Steam has a few of the cars like Volvo 850 Estate but they are European or World editions, not the British Touring Car Championship ones. It was very cheap in the Steam Summer Sale and I'm really enjoying it, even with keyboard. As it's a 10 year old engine it runs effortlessly on modern hardware.
Is this series specifically for GT6? Would you run it in Autumn/Winter so people don't have to decide between outdoor Summer things and indoor gaming things? Also gives people without PS4 something to look forwards to.