Ideally, the regulator should be close to the carb and isolated as much as possible from heat sources. The main reason for the bracket off the car is accessibility. Spliced inline would probably be fine for street use, as long as it is not mounted in a place where any road trash could knock a line loose or something else that would cause a leak. With an installation like Kitz has pictured, both checking the line pressure and making adjustments is easy....