I recently bought a set of STAINLESS steel bumper bolts... They are not actually carriage bolts, but they work the same way... Most of you can get these bolts at local hardware stores... but this is sooooo much easier!!! http://www.carpartsdiscount.com/product/522550A Mustang Deluxe Bumper Bolt Kit, 65-68 $11.95 Fits 1965-68 Mustang. This Kit contains ALL the bolts you need (8 large, 2 small), Washers, and Nuts for the Front & Rear Bumpers. The bumper bolts are hand polished (to a MIRROR FINISH) Carriage bolts. These are Stainless Capped bolts, you will never need to worry about rust again.
I poked around some in there. They've got some pretty good prices. I wish they had more for Mavericks specifically.
Those are nice ... especially with the correct washers ... which are abosolutely necessary unless you want to pop the chrome off your newly rechromed bumpers!