Having watched
some old Wesbank Modified Saloon videos lately, I think going back to such a multiclass formula would not be the worst idea:
The old videos show it only needs a handfull of proper big bangers to make up the big division, import some used V8 Supercars, MARC V8s or touring car-ish GT3s like the Bentley, the Nissan or the M6 for that. Have a secondary division for improved two litre turbo cars from BTCC and TC3 and make up the rest of the field with the production spec cars from the
Bridgestone production series.
I would actually watch that if there was a stream of it, and they wouldn't need to shoehorn everybody in the same engine formula.