[aerohead]

I ran across my GT6 drawing last night. It's definitely pseudo-Jaray, with a very aggressive roofline contour.
By 1989, Porsche was able to get their 911 from Cd 0.40, down to Cd 0.32, with very exacting detail to cooling inlets and underbody smoothing. And it doesn't have the front cooling system penalty of the Triumph.
I couldn't find a definitive drag coefficient for the GT6.
Cds for the Spitfire are not parsed out with respect to whether measured as the top-down roadster, or with the rag-top up.
Carrol Shelby's AC Cobra roadster is estimated at around Cd 0.65.
As the Peter Brock, AC Cobra Daytona Coupe, an estimated Cd 0.42.
As an EV, losing the cooling drag, and smoothing the exhaustless belly, Cd 0.32 seems reasonable.
Skirts and wheel fairings, as with the circa 1962 Panhard Deutsche & Bonnet LeMans Coupe could push the Cd lower.
Extending the roofline, like Carl Breer did with the 1934 Chrysler DeSoto aerodynamic test mule would definitely do it. They got a Cd 0.51 car down to Cd 0.262 as a chopped-off Kammback, and Cd 0.244 with the boat-tail stinger. ( A Tesla Model S in 1934! )