Tom, I just looked at the pics again, the roll structure is only as good as the area it is mounted to. The naked frame pic is the only one that really shows anything. I would want the roll structure tied to more than the top rail. I am not a structural engineer, just a racer. I would want the roll structure tied directly to the top and bottom rails at every point. You might not have to cut it up, just brace it so everything is connected to both, it really looks like a nice piece, I don't see a frame slider so it may be stiff enough and for the money it seems to be a really good start.
If I lived in CA, I would go look at it, but I don't and I don't need another project. For anyone that does, buy it and get to work.
There are a variety of structural guys on this site that can help with what you need to do to make it stronger. I hoped some of them would jump in here and help VF4 make a decision, but my guess is there is not enough info and too many "what ifs" to do an accurate analysis.
VF4, Buy it, start a build diary and ask for help getting the roll structure up to speed (no pun intended here either)