Yeah i would like to do some A-Class and lower racing, cuz its harder to switch from Race Pro to the higher classes. 
U-class Cobra's it is then...

Taking Hop's idea of specs based on the lobby restrictions I went and had a look to see what they are...
CLASS - No Race Cars / D / C / B / A / S / U / R4 / R3 / R2 / R1
P.I - <1000 / <999 / <951 / <901/ (50 PI reductions) / < 151
POWER - <200hp / 200-300hp / 300-400hp / 400-500hp / 500-600hp / >600hp
REGION - Aisa / Europe / North America
MAKE
MODELYEAR - <1976 / 1976-1990 / 1991-1995 / 1996-2000 / 2001-2003 / 2004-2005 / >2005
KERB WEIGHT - <2,055lbs / 2,055-2,500lbs / 2,500-3,000lbs / 3,000-3,500lbs / 3,500-3,850lbs / >3,800lbs
DRIVE - FWD / RWD / AWD
ENGINE - Front / Mid / Rear
So a few ideas for possible lobby based specs...
Club Sports - Mid Engine / RWD / <2,055lbs / <200hp / <751pi
Junior JTCC - Front Engine / FWD / 2,055lbs-2,500lbs / Aisa / 200-300hp / B class
DTM - Front Engine / RWD / Europe / 300-400hp / 2,055 - 2,500
Classic Open - RWD / <1976 / 300-400hp / <751pi
Classic Lightweight - RWD / <1976 / <600pi / <2,055lbs