First, as a poor boy racer, I must say that I personally do not see this as the ultimate solution. While a motor is expensive, it is typically a one-time investment. In my experiences, it is the front end components (axle, spindles, hubs, etc), wheels, and shocks that are the most expensive "disposable" parts of a sprint car. I say "disposable", because I have a rather large collection of these parts that look more like works of art, or garbage, then their intended forms. Even a relatively mild crash is enough to wipe out an entire front end.
Having said that, I would like to submit the following additional information for those who are in favor of this solution. Here is a link to the rules specific to the 305 c.i. winged class that runs on Friday nights at Knoxville:
Knoxville Raceway's 305 Specific Rules
All of Knoxville's rules can be found here:
Knoxville Raceway's Rules Page
I am not trying to be negative about the idea, but I have seen enough races at Knoxville to know the difference just by sound between a 410 and a 360. I have also seen the 305's run on the same night as the 410's, and I can tell you that there is a big disparity in speeds.
Personally, I believe that this is a topic worthy of discussion, and would be an excellent "support" class, but I'm just not sure about turning it into the "real deal" if you will.