maple porter

hey guys im looking for some advise on this recipe i found. ill be doing a maple porter it sounds like a great fall time new england beer. let me know what you think anything you would change?

Ingredients:

5.5 lbs Light Dry Malt Extract
1.5 lbs Crystal Malt (60 degrees lovibond)
1/2 lbs Black Patent Malt
64 oz Grade B Maple Syrup
2.5 oz Styrian Golding Hop Pellets

thinking the maple syrup would add enough fermentable sugars that a smaller than normal amount DME wouldnt make a big difference?

How fermentable is maple syrup? 64 oz seems like a lot.

not sure it was a recipe i found on a google search. i thought it was alot also thats why i posted. i looked through the porter recipies with no luck