Over $6000 to install TTI headers on 66 Barracuda

Hope you're at least getting kissed during this rendezvous & dinner afterwards, as 6k will get you a high-end hooker almost anywhere! Pull the car, find a local race car shop & get one of the guys to work off-hours on it for 1/10 the money & you'll still be ahead! It's THAT simple. Hell, you could tow it down here to Phoenix & you'd still be ahead if I charged you $500, the average rate around here for the job.
Sorry you're in such a bad spot, but you need to step back & realistically look at the spot you're in & make some moves. Your "mechanic" sounds more like a con artist.....