that car isn't much modified as it is 'messed with'. the performer RPM manifold is a great manifold, BUT can only be a benefit w/ other mods. it is designed for high rpm power (hence the name) and the rest of the setup doesn't allow for that. the single exhaust, stock exhaust manifolds, auto trans, probably a stock cam, none of it will allow the manifold to 'work'. right now, it's probably just loud and slow.
I can appreciate the desire for 'original', but that's only a benefit if it's a pre '73. a stock '78 camaro is somewhat less than desirable, as far as performance. stock hp was probably around 135.
performance mods need to be looked at like a combination, not just a bunch of individual parts. a carb and intake needs good flowing heads, a healthy cam, headers, dual exhaust. the trans needs a higher stall converter, and be beefed up to handle the power. the rear axle needs lower gears and a posi to take advantage of the power. then traction becomes an issue, etc etc etc.
EDIT: there isn't any choke on the carb; that carb has an electric choke kit available separately.