So, what can I shoehorn into a Fiat 124?

To keep this on-brand, doesn't the Neon have a hot rod 4 cyl option?

If a Mopar engine isn't a requirement, ever since seeing one in a Locost 7 I've long wanted to do a Quad 4 in something. One of those with the aforementioned T-5 would be awesome and fairly easy to bolt to each other. No idea about fitting them to the car.

Those 124 engine bays are not very big. There's no way I'd try a V8 in one. I'm sure it can be done. I'm equally sure it will not be me fighting how to get it to stay cool on cruise night.