I have been following the discussion on Coupe/Sedan or Modified Sports . . . Talk about a can of worms!
I have some ideas that might make the issue manageable or at least less complex.
You need to start with a set of general criteria that can be referenced when determining if a car is or is not a GT/Modified Sports. Here is a suggested starting point.
The following are considered acceptable for GT and Modified Sports if originally produced as one of the following
• Two passenger roadster with or without additional jump seats
• Two passenger coupe with or without additional jump seats
• 2+2 version of any two passenger roadster or two passenger coupe
• Kit cars and/or Replicas with pre-approval of the SCTA Sports/GT Committee
• Sports racing cars such as those common in SCCA road racing will be classed in Modified Sports classes
The following are considered as acceptable Coupes or Sedans (for Production, Gas Coupe, Altered, and Competition Coupe) in Production, Modified, Classic and Vintage Categories
• Four (or more) passenger (convertible, coupe, sedan, wagon, hatchback, van, suv, and crossover)
• Two (or three) passenger ‘ El Camino style trucks’
• Two passenger special models otherwise offered as base vehicles usually produced for 4 or more passengers (i.e. Mustang GT- 350, Mustang Boss Laguna Seca, etc.)
• Note: See exceptions for pre 1949 vehicles under separate Category rules
If rules like this were adopted the result might find a few current competitors including a few record holders with cars that no longer fit into their current category.
There is still a group of ‘grey area’ cars that slip through these rules such as cars offered as four passenger models in some countries but as two passenger models in other markets. (i.e., Honda CRX)