Oh geez, get rid of those Cobra 4-into-4's by replacing them with any OEM system or OEM front and rear header pipes, and aftermarket slip-ons, and immediately gain 10+% more horsepower! The Cobras are pretty-and pretty-useless for generating even stock or more-than stock RWHP. Swap back to OEM jetting too, to rid yourself of issues with whatever was done by the prior owners' work on the carburetors.