You could get a twin motorbike engined one.
I have worked on one and believe me the twins are not worth the agro keeping them going. The transfer boxes that link the two engines together overheat and shed their oil everywhere. The 4WD versions with an engine driving the front and one driving the rear, just drive plain weirdly.
I had a Westfield Megabusa with a Hayabusa engine in it and its pretty much all the power you need really as standard (180BHP). I turboed mine to 300BHP but to be honest it did not make it any more enjoyable to drive and I was worried about blowing up a very expensive engine. It was flipping fast though :-)
A seven type car with a Busa or R1 engine in it, is a joy to drive on track. I think they are less fun on the road but plenty of people disagree with me.
I had a TVR 5L Chimaera about 12 years ago and that was a lot of fun. I really liked it. Sensible enough to actually go places in but still raw and interesting. I would really like a Sagaris now :-)
Edited to add
I always thought the SEIGHT missed the point of a seven type car, but each to his own :-)