I picked up a used Lyman Mag 20 furnace in a trade and wanted to set up the Mould guide to take Lee 6 cavity moulds. I don't have ready access to a mill nor do I know how to use one. 2 and a half hours of careful filling I was able to open up the guide wide enough to accept the wider Lee aluminum moulds. I also had to relocate the stop plate in the back to let the mould go in further to get access to all 6 cavities by cutting off the back of the mould stop plate and drilling two holes further back on the guide.
I'm not sure if anyone else has done this before (I can't be the only one). I can post pictures if anyone wants to see.