Mike, stop building... put down the welder for a minute... You really need to attend an event and look at what is out there and how others have done things, might save you a lot of grief in the long run. Roadsters have a lot of rules, is your body a duplicate of stock, does it measure exactly the same. Are you thinking Street roadster, roadster or modified roadster.
To answer your question yes there is a class for low power engines, your old hemi does not qualify if I remember correctly, need to have underhead valves or pre 48. You will see all that when you get your rulebook. (I am not familiar with these rules, we have special construction stuff, way less rules than roadsters)
Again, you are in the right place but most of us will tell you to come to the salt or El Mirage and look at vehicles. Study first, build and race next.
Welcome to the forum, there is an intro thread here as well, all the roadster toads
will be entering their welcome.....