I not sure we can really say Blackwing is heavy or "a lil pig of a car" when everything else in the class is within 50lbs. There's a huge difference between being a 275lbs 5'4 couch blob and a 275lbs 6'4 NFL Defensive End and a 275lb 5'7 power lifter.
In a day where safety regulations dictate door cross braces, evap systems, no less than four airbags, and in a luxury car power everything I don't know that BW is fat, it's just big and powerful. I can't think of anything short of a supra significantly lighter. A Darkhorse Mustang tips the scales at 3,913lbs with a manual. 5BW is just 200lbs more with 2 whole more doors, acoustic glass, ect... 4BW is a 100lbs lighter.