Eric,
As you are from Canada, you may be racing in both the US and Canada. In this regard, I would suggest contacting the sanctioning bodies directly, and talking (not just writing) with the technical teams about what you are doing, what is eligible, and what they will accept from not only a roll cage standpoint, but also from a fuel cell perspective. Remember, a rool cage is not just something to keep your head off the pavement, but also to prevent chassis collapse or crush on certain impacts. Each sanctioning body may have some specific opinions on bracing, door bars, etc. Without talking to them directly, you take a huge chance in building something you cannot race anywhere but an open track event. Another question is will the sanctioning body allow the car you are building. Some vintage organizations in the States will not permit a replica. So, research your project to be safe...
Jack