340 exhaust manifold vs stock 318

i picked up a 1973 340 driver side manifold along with a 360 passenger side for $40 bucks so i didnt break the bank. i have a 318 with a mild cam and right now its got the stock 1967 273 exhaust manifolds. wanted to swap them out and was thinking would there be at least a 10 horsepower increase ? i have a 318 with a 600 cfm eddy with a lb4d intake 2.25 exhaust dual. any info will be great! thanks