I have seen several SA Brens, converted locally. They didn't have the magazine well inserts. Not a wise move! The original magazine guides suffer badly and as a result, the FN and L1A1 type magazines get eaten away without the support given to them by the mag well inserts.
Our own L4A1 gun didn't have them either - and used the FN magazines with the small front knib instead of the big hefty block at the front that we use on our L1A1 type magazines. That said, the L4A1 didn't last very long but a few were still around and a whole lot of them ended up as 7.62mm DP L55A1 guns. Correct me if I'm wrong about the DP designation. But it was around that number!