The weight of the car may impact the size of the tubing used. I agree with WeeAsp that a custom welded cage is preferred. They fit so much tighter...in some cases it's like its not there. The kits, in reality have poor fit and you're often tripping over door bars and "A" pillar bars often obstruct entry and vision.
Thanks for the heads up ref. the pre-fab kits. Base upon your info and some side research I have been doing, I will investigate my local vendor options in the greater San Francisco Bay Area and seek assistance with the custom roll cage route.