Hi Kev, are you the same Kev from HMVF? Anyway, MA is 'Made in
Australia' or 'Munitions Australia' depending on your view, and will be Lithgow in origin. JI is John Inglis of
Canada, M/117 is a
UK contractor code for Hercules Cycles, FTR 54 stands for 'Factory Thourough repair 1954'. The Various I, II, II* etc. are the mark numer of the part that is marked.
The top plate is removed by pushing the little button in the middle of the plate down against the spring and sliding the plate off the wider end. Watch the spring flying out and catching you off guard.