Reading the recipe it just screams "Malt Liquor" something I would barely call beer, designed as it is to get people smashed at the lowest possible price.
The Amber dry malt is a good choice, it's the only thing adding any backbone or colour to this brew, in Australia the only Amber DME available is Muntons, fairly expensive by DME standards and as mentioned above not related to Amber Malt but you only need 0.45 Kg so lash out and go the whole half a Kg.
No point in boiling for more than an hour, it's not like there is much in the wort that can be precipitated, nor do you want to. The minute gain in utilisation wouldn't make up for the extra energy used to boil for longer.
I think the recipe is a bit suspect, making exactly 5 US gal (18.9270589 L) and leaving half a litre in the kettle, with the ingredients listed Amber DME 0.454 Kg and Dextrose 2.268 Kg I get an OG of 1.052, at an apparent attenuation of 75% you're looking at finishing around 1.013. The hopping does add up, I get 17.5 IBU boiling at half of the 1.052 gravity.
Frankly I wish they linked to just one of the awards this beer is alleged to have won, unless it was given out by
Modern Drunkard Magazine. Possibly the worst wast of paper I have ever seen!
MHB