Advice for Noob with Slant 6 Barracuda

First, do you really know what high horsepower means? With any engine, max power occurs at high rpm with the engine screaming. To drive like that on the street, you hold it in 1 or 2, or else floor it to keep transmission in low gear. People that drive like that look like dumb kids.

Most people consider high torque at low speed to be "power", like in leaving a stop sign. Think of a H-D blubbing along in high gear and the guy can just twist the throttle to torque his way up. The slant is known for being a torque beast, which is why they were used in full-size pickup trucks and vans. That may be what you really want. For that, a big carb, big valves, and big exhaust won't help much.

First upgrade I would consider is electronic ignition. If your existing distributor is tight (minimal play), you could put a Pertronix ignition in it. I suggest Ignitor II since you can lose the ballast resistor and run a better coil. If you get a later electronic distributor, you can wire an HEI from a GM V-8 easy and cheap, but it won't have the stock look. A used e-distributor is ~$25.

What 1 bbl carburetor does it have? If a Holley 1920, those drove me crazy for decades, giving a rough idle and stalling, until I finally got a good one (4th).