I strongly discourage you from the idea of building a frame that would take really long side pull brakes for 42 tires, because of the long arms, they will not be rigid and braking will be really really lousy, that's why no one does it. You really need to think cantilever or disc brakes. (or v- brakes with special brake levers) I know about lousy braking with long reach side pulls from having walking aid scooters made in China