Are you thinking of doing 1 cylinder- 2 cylinder engines for cars that are not boxer engines. Like in India with small extremely cheap cars they use 2 cylinders. By giving the players this option they can be a company that specializes in very cheap economic cars. Also. Focusing on the car designer. Going back to India car company TATA. Their answer to cheap cars was the Nano which works. So for the car designer give users the option to create very unusual and compact cars.
Also have you thought about having rear/middle mounted engines.
Cars with 3 wheels Etc
Engines will be mountable front, middle, and rear, depending on the body type / chassis you choose of course.
I2s or F2s won’t be in the launch version of the game, but I’d be surprised if we would not add them as DLC later down the road. They are definitely usable!
I cant wait to see what happens…with this game thats exciting I could see some people developing Motorbike engines in this game shortly although it would be crazy xD
Never mind. Remembered it was posted in the FAQ that I3 would be in the release haha. Still excited! 
You can replicate it already in closed beta 
but you’d have to imagine its looks, as no art is done for I3s yet.