Old Stock Ale Extract Recipe

Hello Everyone. So, I really like North Coast's Old Stock Ale, and I found an older post with the recipe listed below. I'd like to know if anyone has tried this recipe and what their results were. Also, the note's to recipe say, "you need to boil your first gallon of wort very hard for 30 to 45 min." What exactly does that entail? Do I boil all the DME in just one gallon of water for 30-45 minutes? That doesn't seem right because the recipe calls for 13lbs. of DME. Please help.

Original Thread: https://www.homebrewtalk.com/f12/north-coast-old-stock-ale-clone-help-98357/

Recipe:
Category: Strong Ale
Subcategory: Old Ale
Recipe Type: Extract
Batch Size: 5 gal.
Volume Boiled: 6 gal.
Mash Efficiency: 72 %
Total Grain/Extract: 13.00 lbs.
Total Hops: 3.0 oz.
Calories (12 fl. oz.): 460.6
Cost to Brew: $49.50 (USD)
Cost per Bottle (12 fl. oz.): $0.93 (USD)

Ingredients
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5 lbs. Dry Amber Extract
4 lbs. Dry Light Extract
4 lbs. Dry Dark Extract
1.5 oz. Fuggle (Pellets, 4.75 %AA) boiled 60 minutes.
1.5 oz. East Kent Goldings (Pellets, 5.00 %AA) boiled 10 minutes.
Yeast: White Labs WLP001 California Ale

Notes
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BrewCrAzY Clone Recipe of one of my favorite big beers. To get the rich
carmely flavor you need to boil your first gallon of wort very hard for
30 to 45 min. Ferment at 67F.

Vital Statistics
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Original Gravity: 1.114
Terminal Gravity: 1.026
Color: 18.24 SRM
Bitterness: 37.9 IBU
Alcohol (%volume): 11.7 %

Bueller...

I should mention I was planning on doing a partial boil since I'm a newb...about 2.5 gallons. Does this raise any concerns?

Your hop utilization will suffer. And I wouldn't be surprised if that much extract in that little volume would become syrup

Good point. Thank you for your comment.

Does anyone have an opinion on which yeast to use? The recipe calls for White Labs WLP001 California Ale, but some comments to the original thread recommend WLP007 Dry English Ale.