The guns are usually pretty tolerant of ammo when using the factory mags. Good aftermarket mags feed well, just avoid Ramline.
An SOT in the US named Norrel made a very popular conversion kit prior to the US cut off of new MG's in 1986. He still has new kits in stock, releasing a few every year at steadily increasing prices. The kit included a modified bolt, trigger housing, trigger, and a new selector. They'd been in production for a few years prior to May 1986, but rumour has it Mr Norrel lived on coffee and very little sleep, cranking out parts just prior to the cut off.
I don't believe any were imported prior to the 1978 ban in Canada.