Thanks for not getting half done before asking for opinions.
Personally, I'd be most comfortable with a Beetle floorpan.
The taper at the front compared to a Ghia/Type III pan will accommodate modern front wheelwells and a beam extender can increase the wheelbase by ~8".
To accommodate the rear engine follow Luigi Colani:
<airframe//powerplant>
You can put almost anything on a VW bellhousing. Pinto, TDI diesel, electric, & etc.
For a pure electric, the Lexus Highlander 68hp axle. For a hybrid boxer or inline three/four, the GM E-Assist serpentine belted 20hp altermotor.
______________
Else, clone Aerocivic.