RE: OS .46LA install
G'day Mate,
4, 4-40 UNC bolts & nylock nuts should be plenty to hold it on, although an OS 46AX, has holes just right for 6-32 bolts, I have no 46LA's so I don't know what size holes are in the engine mounts, but I'm sure 4-40 would be OK, but you can drill them out if you feel the need.
OS recommend 3 to 3.5mm bolts. 3mm is pretty close to 1/8"