lightest a-body??

This is for 67 up stuff, the stuff that accepts BBs without too much trouble.
The weight is not just in the longer wheelbase.The 111wb cars add about 3 inches of roof and floor between the suspension mounting points,over the 108 cars; then, longer overhangs as well. Anything going from the front to the back is also longer; like the driveshaft, the exhaust, the brake/vent lines,brake cables, rear side-glass.Plus heavier bumpers and nicer,heavier interiors..
And the111s often have 4 doors.
The 108wb cars have very short overhangs,and just 2 doors.
2dr Scamps are (Edit;may be) an oddity; they have a short front,a long rear, just 2 doors, and IIRC maybe a 110wb. EDIT:Someone here on FABO mentioned this.