Trying to understand Manifold choices

the stock manifold was and remains a very good manifold. the LD340 is slightly better in the upper RPM range, but on an otherwise stock or warmed over motor isn't worth much more over a stock intake.

a performer would likely be used if somebody wanted to run a different carb and didn't want to modify an LD340, or couldn't find/afford one.

the RPM is bascially the next generation of the LD340.

all are good choices, as are the offerings of weiand and to some degree offy.