I think you can build up to a 604" motor out of a Mega block.I have never seen one on the street.I don't believe many people will build a big motor like this and put it in a stock apearing car. Unless you have a huge payout to pursue. Then you will attract special purpose built cars. I just want to run my street car in a heads up race.My car is my cruise night Sunday driver. It even has air conditioning.I would not build a car special to meet race rules just to possibly win a few hundred dollars and have bragging rights. The bottom line is to attract alot of cars the rules need to be broad enough that many different setups will be allowed to run.
I think the best way to equalize the field is with the tires allowed. No slicks allowed.