Magnum exhaust manifolds

There is a dyno comparison of the different types of manifolds and short and long tube headers on a mild 360
Long tube headers obviously produced the best results.
To me the difference in the rest didn't matter much about 5 horsepower between 318 manifolds and the short tube.
If I remember right the best manifolds was one 340 and one magnum. In your case you'd be lucky to see 2 hp