Why even change out the components, instead, just use the complete SIII axle? I can't think of any difference between the axles between a IIa and a III, per se... if you were switching from an 88" to a 109" rear, then the drum sizes, etc., will be different, or you might even find a Salisbury, but say, a '67 88" and a '73 88", should be the same....
RN will have suitable ones, but, you should be able to locally source ones that would work if you know where. Ubolts aren't magic. What kind of paras do you have?
-L
'72 SIII SW 88"
'60 SII 88" RHD