You might have to get a shorter bolt of the same thread pitch and diameter. I'd also make sure the air conditioning unit (or whatever the bolts are connected to) is supported with a Jack stand or ratchet strap, etc, before loosening. Unless it has nowhere to go anyway, of course. Keep the bolt length as long as possible but shorter than current bolts. You want as much thread engagement as possible.
-Travis & the DawgBüs
<<1982 E-350 cutaway, Collins Bantam ext. body, Maximum 4x4 F-350 drivetrain conversion>>