351M had a dry intake manifold, ie thermostat is in the block, 351W has a wet intake, ie thermostat is in the intake.
351W has a 3/4" lip right behind the distributor (Taller deck, lip extends block up to the bottom of the intake) and a 302 has hardly any lip at all behind the distributor.
Go with what you've learned from the firing orders in this thread. Just cuz it's a 351 doesn't mean somone didn't throw a 302 cam in it, or vice versa. Like my Dad always told me, "NEVER assume the idiot that worked on it before you, knew what he was doing."
Good luck!
