So I figured I'd try to find the car I remembered with a Porsche engine in it so I got out my "Lotus Seven & The Independents" book by Dennis Ortenburger, and there it was on pg 165. It was called the Portus and it was built and autocrossed by Del Long in the 1980's. Surprisingly, the car started out as a Lotus Seven Series 2 with the 948cc motor and was upgraded to several Ford motors, then a Porsche 914, and finally a 911 motor. From the pictures in the book, you can tell that the front frame was widened to fit the flat-6, and the motor had two 3-barrel Weber downdrafts with what looks to be K&N air filters sticking through the hood. Unfortunately, they weren't the bigger 3.0-3.6 litre air-cooled motors but were limited to 2.0-2.5 litres depending on which class he was competing in.
I couldn't find any pics of the Portus on the web so I figured I'd show you one of Long's later creations which was a D-mod Locost powered by what looks to be a Honda or Acura motor: