The BEAM is irrelevant as no part of the ROLL bar attaches to it, it is secured to the chassis, and then at the ends of the roll bar by drop links to each ARM.
These attachment points on the arms are INBOARD on the sapphire arms and OUTBOARD on the 3 door arms that is why the 3 door roll bar is so much longer.
Unless you are moving the attachement points on the arms, to suit the roll bar being used yopu can only use the correct one for the correct arms.
The sapphy bars are held to the body by clamps either side of the diff area on a flat chassis section.
The 3 door bar is held by clamps right near the top of the spring, about 1 1/2 feet away.
tabetha