Exhaust limits/Carb choice
If you're gonna use the manifolds, why don't you try to find some 68-71 340 abody manifolds. they'll work better than the ones you have. Sell the headers to someone who wants them more than you. Personally, I'd use the TQ, but you can't find jets or metering rods. You'd probably be better gas mileage wise with a 600 vacuum secondary Holley, or maybe an Edelbrock carb. Good luck. Sure wish I had a cool dad like you when I was 16.
don