[Too Many Projects]

Sounds like your garage is sealed pretty tight for the climate control and may be part of the issue. It can't breath and let some of that smell/air get out.

All the '69's in your sig should have non-vented gas caps. If any of them have vented caps, they should be changed. You could try putting tennis balls in the tail pipes to prevent the odor from escaping from the exhaust system. Normally, I wouldn't suggest sealing them, but with the A/C, the air should be dry enough to prevent condensation. Maybe try that for a few weeks and see if there is a difference in the level of the odor.