They did several modifications to the Mk.2 bren to convert them to 7.62 X 39
Interesting this has popped up as I am currently doing some photos of one but my recent accident has caused no end of problems in completing the project.
There was also a CzechZB 26 converted to 7.62 X 39 conversion done as well, and I have had the pleasure of handling both and firing one of them but that was many years ago, so I will have to scan the photos
for the net.
There is a decent write up in the BREN GUN SAGA, second editon, by the late Tom Dugelby.