my mistake you are correct and i belive its a 10mm bolt, so going to a junkyard would be the best bet.

Update - a year and a few months late but just posting to say thanks all.

I did find that tapped hole, but all the Blazer's at the junkyard were on the ground so no access to the bracket. Got my filter on anyways a few days after my last post.

Once again, thank you!