I doubt the axle manufacturer is going to help much as that axle could have been used with several different brake and hub assembly configurations.Your best bet would be to remove a stud and measure it to match it up .Remember the driver side uses left hand threads while the passenger side uses right hand threads these coaches used bud style wheels with spherical ball nuts which are different front and rear.Your going to find that the parts guys aren't going to have any idea what was used on your chassis as the Magnum chassis was an in house build by the Safari Motor Coach company the builder at the time of the Beaver Coaches.https://heavyparts.com/media/docs/LASCO-Dorman-Lit-Pernos-Tornillos-y-Tuercas-de-Rueda-hd-wheel-hardware.pdf