I drilled out the holes in the perch on mt R75 and inserted a 10x1.25 helicoil, but I suppose I could have just drilled and tapped the hole as mine had a 8mm clearance hole.
But I like inserts in alloy.
It will give you a much better choice of mirrors, 10x1.25 mm RHT is the industry norm.
I found a good quality pair of mirrors on Ebay, made for a Kawasaki Z1 - look and perform just like the OEM mirrors on my G/S and GS but cost around $17- each.
Adelaide Hills, Australia. 93 R100 GS, 77 R75/7 ,70 BSA B44VS, , 86 R80 G/S PD, 95 BMW Funduro F650 ST