Get a 1 1/4 and bore it out, it will take it, you are only talkin 1/16 each side, you could even file it with a half round file, zinc is very soft, you may get down to the backing, but thats no problem. There will be at least 1/16 covering the backing. If you don't have a file suitable, it might be an idea to buy one, you're going to need it again! You could also buy three or four and get them all bored by your local friendly machine shop, it'll take them minutes with a pillar drill and 1 3/8 bit.