Ok, so I ran down to my usual mower parts shop, which is a Briggs Performance dealer, but the guy says that they don't make keys for the 11hp Briggs.... only up to something like the 8 or 8.5hp models because they're commonly used for Jr. Dragsters and Go-Kart racing (ok, that's understandable I suppose).
He says that from what he's heard, many people in my situation wind up grinding some keystock down to get things where they need it..... which sounds like a royal pain in the butt to me.
Any chance that you've got something for my application kicking around, or know where to get it online? (25 series, 11hp Briggs)