I can't find much out there on these, Blue. A couple of Mini & Alfa forums mention them, but they appear to have been pretty low production, '70s vintage wheels. Supposed to be pretty light though.
Magnesium? Who knows. You should be able to scrape off a sliver from the inside and hit it with a torch. If the sliver ignites, it's Mg. IIRC, Mg also reacts with vinegar (bubbles). Less spectacular, but should be telling.
Fred
Tampa, FL
'74 260Z 2+2 Auto, 102K. Daily Driver. Mods: SU RoundTops, MSA Type II Body Kit, Twice Pipes, ZX Dizzy, E12-80, with MSD Blaster II Coil & MSD Wires. Tokico HP struts & lowering springs.
I have a set of the exact looking wheels.Mine are 5Bx10 they are going on a 1972 Honda 600 sedan. I was trying to find out what company made these wheels. If anyone knows anything about them I'd like to hear it because I'd like to find another set. It's the only custom wheels I've found to fit my little Honda. 10 inch dia. wheels are hard to find.