I looked through my rat's nest.
*I think the 'naked' Dart is around Cd 0.485.
*It's aft-body is about 42% of the A.S.'Template' II.
*An approx. 4.8-inch rear deck extension(4.8" beyond the trunklid) would bring it right to the 'Template',so I'm reversing myself when I say it would be okay to do a serving tray type spoiler.
*At 42% of the 'Template' the Dart has the potential for around Cd 0.192,with all the whistles and bells.
*The 1991 GM Ultralite is 42% 'Template',with Cd 0.19.
*The 1956 Dodge Dart concept,by Ghia,registered Cd 0.17,at 63% of the 'Template.'
*basjoos' 2005 AeroCivic is Cd 0.17,at 50% 'Template',with its beautiful wheel integration.
*A 'Template' car,at 63% would come in at around Cd 0.149.