If you want to go "full race", a car motor is the way to go. The NovaRossi "Roma" 25 bears a strong resemblance to the favored but scarce GO 25, and new ones can still be had. I have one but have yet to do anything with it. I've also had a Mockingbird set up for AMA slow rat, and was able to run in the 16's with both the OS25FX and the Webra 25.