Here is a list of what I have discovered to be convertible thus far-
Coupe: Ubermacht Zion Cabrio, Ubermacht Sentinel, Lapadati Felon GT, Enus Cognoscenti Cabrio
Sports: Dewbaunchee Rapid GT, Grotto Caronizzare, Obey 9F Cabrio, Benefactor Surano
Sports Classic: Dexlasse Tornado
Compact: Weeny Issi
Let me know if I missed anything, hope this helps someone else as well!