Many very nice classic cars have been lost to fuel fires. A very small leak, just a few drops on warm engine can generate very strong odors. As mentioned, I would not park inside, certainly not in a basement garage, gas fumes settle and travel downward.
Start at the car carborator and work your way back to the tank. Look for staining caused by fuel. Check The rubber hoses first then steel lines.
Small leaks can be tough to find. Good luck. Keep a fire extinguisher close by.