drill the new guard to suit hopefully getting it straight
. I start by drilling the front one very central and smaller than 1/4" - 3/16"? 4 mm.?
. Then I bolt it to the front of the brace and check that the 'guard is central between the fork legs; if it isn't, because I drilled the hole in the 'guard smaller, I can file one side or the other to get the 'guard central before I open up the hole to 1/4" ID.
. Another reason I start by drilling the hole smaller is drilling a hole in sheet metal, it comes out trochoidal.
I open up with a conical burr so the hole ends up circular, even if filed the original oval to move the 'guard on the bracket.
. Only when I'm happy the 'guard will appear central do I open up the hole to 1/4". Then I bolt the 'guard firmly to the bracket with the front bolt before drilling the two between the fork legs (again starting smaller and enlarging to size).
Before you buy the bolts, both my T160's came with soft vibe-isolating washers between the bracket and the 'guard, although they aren't shown in the parts book. I was able to buy more many years ago, 'fraid no idea - apart from possibly a long-time dealer - whether they're still available under whatever the part number was. Or you could possibly add off-the-shelf plastic or rubber washers?
Also, the spec'd washers in the parts book were the Imperial equivalent of modern 2 mm. thick - this is unusual as common 1/4" washers are/were only 1 mm. thick/equivalent.
Personally, not a fan of mudguard mounting bolts protruding towards tyres, I replaced with ordinary stainless hex. bolts fitted from under the brace/'guard, topped with stainless domed nuts outside the 'guard.