Reply to "Smelly Cat....Smelly Cat"

Is there any evaporated gasoline residue on the intake manifold? Rusty color?
I had a rebuilt Holley 600 or 650, anyway, a rubber o-ring let gas trickle out and it formed a pool of gasoline on my intake manifold. I went to an Edelbrock carb, with no external gaskets or o-rings below the float bowls. Fixed it, no more leaking, but any new carb will fix that leak, it's just nearly impossible to rebuild old Holleys, that O-ring is notorious for leaking after the rebuild, and mine had "A Professional" rebuild the Holley. Wanna buy it? Then you can have two leaky Holley rebuilt carbs. LOL!

Have you inspected your mechanical fuel pump?
It has the ability to leak, and could potentially leak your entire gas tank in siphon effect if the rubber bellows is cracked around the perimter edges. The fule pump is mounted below the fuel tank fuel level, and can leak out all that expensive gasoline, dude!
Or if you're even unluckier, it'll just simply fail on you 300 miles from home. It's so cheap, a guy should just simply replace it to make sure it's not causing either "the smell of gasoline problem" or "the failed fuel pump problem on the side of the road." Spend the $30. Spend the 30 minutes. Eliminate the risk.
It's also a fire hazard, when it reaches lower explosive limits. Isn't your garage ventilated? Where I'm from, the pilot light on the hot water heater is the ingition source. Hot water heaters are many times located in a closet inside the garage, and the closet door is ventilated to the garage, which is where I think you say gasoline fumes are coming from. Dangerous possibilty happening. Warning. I'd crack the garage door an inch or two until the riddle is solved, and I'd replace the hoses, as mentioned, which I'm sure you did already, but change the fuel pump for cryin' out loud.
Skip the movies and work on the cat, the old lady will see the wisdom, I'm sure!!! Fire hazard in her house??!!!!! She'd make you sell the Pantera if it caused a fire, Amigo!!!! Skip the beer, or take baloney sandwiches, but change the fuel pump!!

Seriously,there's every reason to do it and no reason not to. Process of elimination.

To answer your other question, a check valve in the vent line is OK, but ask the Pantera vendor where to instal it. MY advice is install it right at the very top of the fuel tank, where the vent hose is connecting to the tank. See? You didn't need the ventilated gas cap after all.

But you do need a fuel pump, unless you've already installed a new one, and it's been two years now, with temperature cycles hot cold hot cold...put VERY, as in VERY HOT, VERY COLD, in front of each of those temperature swings.

LOL!!!!! No fires allowed! You need a NO SMOKING AROUND PANTERA sign up in the garage until you fix this, lest the sister-in-law have a gander at the Pantera whilst you'ze at work and BOOM!!!

All kidding aside, let us know the status, and we'll give you some more colorful hints about them vapor smells. My Pantera don't smell at all, and I just went and sniffed it, up close to the engine screen, just for your very benefit, Amigo!!! The dogs were watching and saying "I know what he's doing, he's sniffing and I know why he's sniffing, I just didn't know where to sniff, did you Brutus?"
The hot, clicking, wide open throttle smell goes with the territory in the bad boy toys, and goes away by the time you wake up the next day. That's the headers, and they're hot, so watch your gasoline hose routes by them headers. No zip-ties of the gas hoses to the headers!!!! Sorry, I'm being mean now, and I know you're an engineer and engineers don't like jokes, so I'm sorry. No more wise a$$ jokes. You can hit me back next time I have to ask a question and I'll know why you socked me like that when you do it, won't I???

your wise a$$ buddy,
Ron