Looks interesting. Just glancing at it, the extract does seem a tad on the low side, but I suppose that will depend upon your mashing efficiency with the pale malt. As you say, easy to correct for. Run it through some brewing software or the Recipator to check the numbers. Otherwise, it seems a fairly straight forward Brown Porter.
One thing worth mentioning, when I was doing some searches for that book, it received fairly negative reviews on Amazon and the like. Some folks said the info it contained was patently false in a few cases. I did, however, find this site, which had a really nice writeup on the details of the Catamount Porter, and even a pic of the label:
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The core info there is 5.8% ABV, 30 IBU, 1.060 OG, 1.014 FG, and Nugget + Yakima Golding hops. That info is pulled right off the label/extrapolated from Harpoon, so I'd lend more credence to their take when compared to the recipe book. Here's their write-up:
The Catamount Porter is a dark, rich, brown porter with a thick & creamy tan head. It's brewed with no less than seven different types of malts along with Nugget and Yakima Goldings hops. We found it a hugely aromatic brew, slightly sweet, with a big roasted coffee nose which also hinted of chocolate and caramel. Look for a very creamy and smooth mouthfeel. The flavor profile is complex, bursting with notes of coffee, chocolate, sweet malts, caramel, and roasted malts. There is a slight hint of the citrus hops in the moderately dry finish.
A perusing of BeerAdvocates 25 reviews on the Catamount Porter agrees with the above blurb.
So with that in mind, I'd say an approximation (or an interpretation) would be a tweaked version of the recipe I posted, with the chocolate bumped up to get some of that coffee effect, and an 8 oz 120L addition for complexity. I've edited it to reflect the changes. The one from the recipe book doesn't seem to come anywhere close to capturing everything that the Catamount is supposed to be.
Either way, I'm pretty excited to brew this one up. It's bringing back a ton of memories from my college days.
Good luck with it, and let us know how it comes out whatever way you go.