Whats 340 about it, the 1 7/8? I had a service manager work with me and he told me they stocked/produced stock for 7 years after production.. some sort of regulation...could have been blowing smoke.
The casting number (3418623) and the size of the exhaust hole is the only way you can tell a 340 (like this one) from the regular non-hipo manifold. A regular non-hipo 318 manifold has a 1 5/8" as opposed to 1 7/8".
Unless someone else has more/better information....
Treblig
