Hmm, that's a conundrum?
The fastest "track" black cobra I know currently is Geoff Tauntan's BDM. He can be contacted through BYDesign Motorsport but I don't know whether he's the guy you're chasing. Gary Halls BDM is only a flys *(&^*( off his pace.
There's a another fella called called Mark Crespan who I think owns what was a FLURO green and now black cobra called the MONGREL Cobra. he doesn't swim on the Club Circles but moreso the historic/sprint circles.. He's often at Leyburn and Pittsworth sprints etc. Mrs Flatchat on here would certainly have his contact info and know some more about the car.
See below
Oakey Street Sprints Grant Watson driving the Mongrel Cobra - YouTube
I've never seen Marks car tracked so don't know what constitutes fastest.
The quick BLACK Cobras I know of are...
Wayne Proctor's Harrison
Gary Halls BDM
Geoff Tauntans BDM
Scotty Hampsons Custom build of bits
And John White's old Turbo Car which is now are beautiful street car.
Wazza Red car with mud on it (looks black) is pretty quick too.
Regarding what you are trying to achieve it sounds more practical to modify that castor angle than try and compensate for it but that's only my opinion.
Good luck in your search.
Spookypt