Welcome to the site!
I moved your post to our Street Legal Legends section.
I know they race Legends at Evans Mill Speedway.
As far as making a legends car street legal; Yes, it can be done (and has been done in several states). Not always without issues, as you will see if you read Dennis's posts on his fight to make his legends car street legal in Texas. Some states are easier to title and license a car than others.
As far as fitting 2 seats; You have to remember the size of these cars. The chassis is only 3 feet wide. Also; The drive shaft tunnel takes up space on the right side of the interior. So side by side seating isn't really an option. You could possibly stretch the chassis lengthwise and add a seat behind the drivers seat. That would involve a ton of fabrication work!!!
Probably not what you wanted to hear. But you would certainly turn heads cruising around town in a street legal legends car!
Steve