What seems to be the problem with 7.62mm magazines for the 7.62mm L4 Bren conversion. If you haven't got the 30 rounders, then the standard rifle magazines fit and function - as they were made to interchange. And even if you can't get the UKicon 'big lug' type, the FN type will fit. And if they are a bit loose fore-and-aft, then it's simplicity itself to fabricate the big lug.

Or am I missing something in my old age?