The 409 was the big block Chevrolet engine from 1962 to 65, which replaced the 348. Both engines have M-shaped valve covers. The 348 was a last-minute addition to the 58 passenger cars, when Chevy got tired of their 57 model 283's getting outrun by Ford's 312 engines. The 348 was originally intended to be a medium-duty truck engine, never supposed to be used in cars. A solid lifter camshaft and 3-2-barrel carburetion helped the 348's catch up to the Fords- - - -until the Ford 390 came along!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!