Probably the stock Renault R16 engine. It produces enough power, plus the car only weighs about 1400lbs with engine.

However, this car is 2 behind. I'm working on my 69 Datsun now, with the goal having it completed by late Spring of 2010, maybe early summer. Then after that I'm going to finish up my 1990 RX7, then I will get to the Lotus