I've received a bunch of the GMac brass transfer ports.
They're 1.6mm bore, which is smaller than even the Canadian spec restricted ports.
The 3mm port I've got in is perhaps a little much, the power is up in the high 5's
So I'm going to go to 2.5mm as a starting point and see what happens.
The GMac ports are brass so are easy to drill out. I'll just use my drill press, rather than the lathe.
I'll post when I've got test results.