We're almost at the end of the Willie line! After this ad, I have only one left. Although admittedly I have not yet scoured every issue of the New Yorker between 1940 and 1965 so it's possible there are others...
I can't find any definitions for "see a fox" that remotely match this ad's context - the artist seems to be indicating that the "fox" is perhaps the sunrise? That would make sense in connection to "the sun's over the foreyard" which according to A dictionary of slang and colloquial English means to drink before noon.
According to Ahoy, Mac's Web Log:
The lead line is a length of rope up to 50 fathoms long, ( a fathom is the term for 6 feet ) and this line is fitted to the lead weight, hence the expression "To heave the lead" which means to use a lead line line to find the water depth. This should not be confused with the term " Swinging the lead" which is used to describe a sailor who is lazy."
Naughty mind that I have, I can think of another definition of "swinging the lead" - or is that pipe?
We already know about "plush" from a previous Willie ad.
According to Boy's Life, December 1927:
The shack locker was a sort of pantry in the foc'sle where the men took snacks between meals.
And I don't have to tell you loyal readers what kind of "snacks" Willie likes best.
But what's a "foc'sle"? That just means forecastle, which is according to Wikipedia:
Forecastle refers to the upper deck of a sailing ship forward of the foremast.
The Free Dictionary pronounces foc'sle as "foke-sul".
You're gonna wow them at your next cocktail party.