1992 was not on "FIA Super touring".
I don't know well about Super touring (between GroupA and FIA Super touring) but according to list of entrant
they seems permitted entry with 2-door cars.
Anyway, I might be too match particular about door numbers, I feel strange to call 2-door 320 as STW-BTCC.
Yes, the SuperTouring was born in 1990 in Britain. From 1993 it was a main national level touring car class: Class2. (The DTM was the Class1)
In the regulations I can't found that the cars must be 4 doors. But mention somewhere the rear doors.
http://www.supertouringregister.com/regulations/
Anyway, that relased car is not a Supertourer from 1997. The exterior is a road car with an e30M3 wing and rims. The cockpit is good racing cockpit, except the complety road version dashboard, and the inner part of front doors. So for me its is looks like an gr.N or gr.A modified car. But very fun to drive
Tomorrow I will test it agaist the PM3DM touring cars (Primera, Volvo, and the (real) BMW STW)