Unblown flat-four in front with a bug-catcher; Studebaker cab back and Porsche 924 transaxle in back.
Blackjack Zero with front/front. 2CV-based car in the rear.
Motoguzzi V-twin in frontwheel drive.
The V-twin [probably] would fit in the front sheetmetal and bumper.
Edit: has anyone else noticed that skippo bumped this thread from 2012 and hasn't posted since.