I personally wouldn't cut sheet metal. If I were going to, I would completely cut out the vent and shave that areap, then fab up a couple of sheets of MDF glued together and shape them to angle the speaker appropriately.
If you're gonna do it, might as well do it "right". Half ass job == half ass truck.
__________________
If I've got anything up for grabs, it'll be here: 7-hole gauge cluster for a 67-72 p/u FREE (
link)
I can't check the forum daily. If I don't reply to you within 24 hours,
drop me a PM! I'm (hopefully) still alive and will reply faster to a PM.