Hello Butchy8

Your Morrison is, itself, based upon the British Ransomes Minor MK7.
I have explained that here: -

https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=72511

Yes, the first Masport 500s should be identical.

https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/85624/Masport_Olympic_500_cylinder_m.html

Hope this helps.
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Jack