Need Help With Engine Diagnosis

Sorry for the long post, but I figured you’d need specifics. 69 Barracuda, 340, 4 speed, 3.55 gears. About 15,000 miles on 12 year old rebuild by myself. Comp 268XE cam lifters and springs, headers, Eddy Air Gap, 750 CFM Eddy and MP ignition system. For years, I could melt the tires with this combo, and it drove great. In 2013 I blew the car apart for a complete restoration. There was some coolant leaking under the heads, so while out of the car, I replaced the head gaskets. The car is all together now. It starts right up, it idles fine, and it cruises down the road OK, but it doesn’t have near the power it did. I have to slip the clutch more than before from a stop or the engine bogs, and if I stomp on it, it falls on its face and sputters at about 4000 RPM. I put in new plugs, the timing is set at 33 degrees total at 2500 and I put a can of Sea Foam in a fresh tank of gas. Per a suggestion from Mopar Performance years ago, I unhooked the vacuum advance. It ran fine without vacuum advance for years. It acts like either fuel starvation or ignition. I thought I’d start off with a compression test and then replacing the fuel filter. Is there a way to check the MP ignition system? Also, can a carb go bad and cause this by sitting around for three years? I’m pretty sure it isn’t a head gasket, because the oil is clean, and with radiator cap off there is no surge in coolant.
Thanks in advance for any help.