Powering a car with a motorcycle engine is a bit more complex than dropping a smallblock Chevy into your old street machine. Motorcycle engines are not equipped with a transmission containing a reverse gear or motor mount placements designed to work with a car so any of these motorcycle/car hybrids are going to be custom built the first time around. If you're comfortable building one off prototypes, you can start from scratch. Otherwise, you can take advantage of those who have done this before.
