Any place we can find the rules on cages for road racing?
Depends on who you will be racing with and what class you will be racing in.
Sanctioning bodies all have their own rule sets that apply to everyone racing, regardkess of class. These are sometimes referred to as the "GCR" (General Competition Rules) or "CCR" (Club Codes and Regulations).
After that, each series can modify those rules to suit their own needs.
Of course, if you're not racing and just want to do open track or HPDE events, you need to check with the event organizers to see what they require.
In general though, if I wanted a road racing cage, I'd get a copy of the NASA CCR
, and study the section on safety cages, seats and seat mounting, and harnesses. Take all that knowledge and the rules to a reputable cage builder, and have him build a custom cage to the NASA CCR specifications.
I am NOT a big fan of bolt-in cages -- I've seen too many fail.
I'm also not a fan of letting a sloppy or inexperienced fabricator building a cage. You are betting your life on the design and build quality of your cage. This is not a place to save money.
How do the MM roll bar kits stack up?
Never looked at one close enough.