Need help with semi auto L4A4

[Kev G]

303 locking shoulders will all be to big for a 'standard' L4A4 and if grinding down will probably need re-surface hardening.
Have attached info on locking shoulder sizes for reference.
303
Attachment 114785

7.62
Attachment 114786

As others have said this is not an Enfield or Interarms barrel but would be interested to know how many grooves the barrel has ?

Not that it has anything to do with your problem but S/N A5197 shouldn't be dated 1967 as it was a batch of 180 L4A2/L4A4's dispatched to Weedon in March 1960 ?