There is some...key word: some okay is Group A mods but some looks wise are crap the ATCC Group A's drive nice but looks subpar to other Group As like the E30 (which is ironic cause that's kunos), You got Bazza's AC legends Trans-am mod which is fantastic to be fair. I believe there is an okay ish Tank (volvo 240 Turbo) out there but i can't remember if it was made by ATCC or somebody else. I know a Starion for Group A is out too. The best Group A i've seen atm is the Cossie which is on RD
^ this doesn't count Tommy78s Group A DTMs
I know ATCC did the Aussie Group C touring cars which is 70s/80s before they started Group A cars in the championship
That's pretty much what I said : a properly made. You have a bunch of cars from different years, with a quality range going from crap to gold, and some modders (thanks to them) were able to balance them in a racing serie : the atcc A and C are quite good, but with a lot of problems and lets be fair, quite ugly for today's standard. Bazza's TA is really good too, especially on the physics/BOP side, but he has to work with what he got : some models are nice, other's seriously old, and most are not race-prep (racing in full customer-ready interior is... not efficient, to say the least). I did my own "trans Am" serie with I-don't-remember-which Mustang I had, a beautiful model, full race prep, superb sound, but a bit too modern physics so I tweaked it a bit, and combined with a Camaro I like (one full race prep, really "old school racing" looking), that I had to modify quite a lot to enjoy (physics, sound, shaders, etc).
Racing the 70's or 80's touring scene is not a problem in today's AC, but we are still far from the quality range delivered for F1, GT3 or modern LMP's. And it's mainly because of public interest. We're a niche, that's all ^^
On a brighter note, VRC's release of late 90's BTCC combined with the ones we already had from F302, PM3DM and co., with the quality of the british tracks around, is even more than we could ever have hoped for.