Maple syrup is approximately 11#/gal (1.375 oz/fl oz).
Previous recipe called for 3.5# maple syrup or 41 fl oz per 5 gallons. Scaled up would require 4.2# maple syrup or 49 fl oz.
Since 1 qt quality very dark maple syrup is approximately $22 or 1/2 gal is $43. I suggest 1 qt of "very dark/grade B" and 16 oz D-45 candi sugar to augment syrup. Candi will lend vanilla and toffee notes.
1 qt / 32 fl oz / 44 oz by wt
Maple Syrup additions:
1. ) Whirlpool < 180'F : 27.5 oz by wt (20 fl oz)
2.) Secondary: 1.5 cups (12 fl oz) or 16 oz by wt
I suggest buying "Very dark/robust taste/Grade B" from one of these two links below: