A "318" would be a 6V-53 Detroit Diesel, wouldn't it? The 1954 GMC 630 I drove to Kansas City had a 503 cubic inch gas engine with the dizzy on the driver's side, and an earlier version of that one was a 426. I don't know if there might have been a displacement in between those sizes or not. The 503 had a big Holley 2-barrel with a governor on it.
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!