[aerohead]

I'll join the :ditch the Midget,go with the Spitfire club,and for the same reasons mentioned.I've got a Spitfire out in my yard that a neighbor has expressed interest in.I'd keep it,however already too many projects on the stove.While a better starting point than the Midget,the Triumph is completely dirty below the beltline,all the way around the car.I'd consider a wrap-around nose,to get air around the car,rather than under it.Go as low as you can without striking driveway ramps and the like.Deep (tall) rocker extensions between the wheels would help attached flow down the flanks.and keep flow from crashing into the spinning tires.An extension behind the rear wheels would help clean flow to wherever you make the end of the car.If the fiberboard radiator duct has survived,that can be integrated into the new nose.Clutch-fan? Flex-fan? Electric fan? Those aftermarket hardtops pictured are beautiful,and way better aero than too-fast factory fastback.Short of new roof,you could simply lengthen the car at boot level with a horizontal spoiler ( no upsweep!).A horizontal wing ( ala Sierra concept/Merkur XR4Ti ) centered on and touching the rear window would help flow re-attachment,entrain a couple vortices,and give more ideal flow over the boot.As far as the bonnet,you might soften the collision of air at the base of the windshield with some form of blister that you could see over.The whole "rake" of the Spitfire pictured seems reversed from what you'd want.The nose should be down,not up,unless it settles when you and a passenger jump in.Some sort of perforated disc wheel covers would help a fraction.Having the petrol filler neck where it is makes for special safety consideration.As far as the Triumph's Cd,I believe there was discussion of that over at maxmpg.You'd have to fish around for the info,.but you might want to check that site.