I suck at sawing holes in wood so I've scored a Dewalt 86mm hole saw- perfect for the GIS lug mast holes. Got it from this bloke below.

DEWALT 86mm (3-3/8") WOOD OR METAL HOLE SAW LOW POSTAGE | eBay

Or, once I'm finished with it, I'll be happy to sell it for $25 including postage. I all ready had the auger from another hole saw set bought from Bunnings.