Actually it's more than just
baseline physics, but it's not as impressive as you might be thinking. I've had the 512 going for a year and a half. The Diablo at least 6 months. And the 993 was ~75% done last year when I set it aside after the Porsche license announcement. (That one was a Turbo, but working backwards to a C2 wasn't so tough.)
As for sources, nothing unusual. Ferrari and Lamborghini were kind enough to put very nice drawings of the suspension in their service manuals. I have accounts at relevant fora (FerrariChat, Lambopower, et al) which I've combed thoroughly for data. Both of them are among the cars for which I have had the most complete data set.
The 993 is also pretty well covered online. Porsche owners are by and large a pretty technical bunch, so there's plenty of good data out there. Lots of useful threads at Rennlist - much like my WRX, a lot of contributions came from the autocross crowd. They're an analyzing bunch. Many charts.
The Viper is currently on a provisional suspension geometry pending better data if possible, but the measurables are solid. I may take a chance and order a service manual... haven't had luck finding one online. I doubt I'll be able to find an owner to measure for us.
As for the RX7, the Spirit R is 7 or 8 years newer than the rest and it's not
really the right car. Ideally we'd have the base model. But it looks like it will work nicely in class 2. Dan tells me that the 993 was always a bit slow in the original game, so maybe it's always belonged in class 3 anyway. A perfect swap.