Well the SEAC could be a WO1 and the ASM is a Capt so SEAC salutes ASM, Or the ASM could be a Capt and the SEAC a Maj so ASM salutes SEAC, then the ASM a WO1 and SEAC a Maj so ASM salutes SEAC, or they could both be WO1s but that would just be silly.
The badges of rank would consist of the Royal Coat of Arms, in a wreath, surmounted by a representation of Buckingham Palace in turn surmounted by a likeness of Her Majesty's face. The rank badge would be too big to fit on the uniform, so he would be granted a Colour to bear it on. This would be carried on all occasions no less than three feet from QSM Haughton by his Private Orderly Officer (QSM POO).
This POO would be the most senior private soldier in the British Army, and on the accomplishment of six months satisfactory service would automatically qualify for an RSM's pension.