Converting rear drum brakes from SBP to BBP

in vehicle now is sbp "MOSER" axles ... i was going to have these redrilled to lbp and then upgrade to F body backing plates and drums/shoes ... i asked Moser about axle length when comparing SBP and BBP .. he told me they were the same length ... ?? I will ask again ..

The axle length isn't the problem, the axle flange offset from the housing is different. You can not use BBP backing plates or drums with SBP axles regardless of the bolt pattern you have drilled on them. If you're currently using SBP brakes you'll have to have those drums re-drilled and re-use those brakes if you have the axles re-drilled.