I found this:
Malts: 2 Row, Munich, Carastan 30-37
Hops: Centenial, Cascade
Back of the envelope:
5.5 lbs of Light DME (or 6.5 of Light LME)
1 lb of Munich
.75 lbs of Carastan (or another medium/light crystal if you can’t get Carastan)
The Munich has some unconverted starch, so it would be best to do your steep in just 3-4 qrts of water, try to hold the temperature around 150 for 60 minutes (then proceed as usual).
I would guess it is around 35 IBUs. The exact amount of bittering hops will depend on the size of your boil and the alpha acid of your hops. That said with a full boil I would go for something like
1 oz Centennial @ 60 min
1 oz Cascade @ 5 min
1 oz Centennial @ flameout
(you could even toss an ounce of dry hops in if you wanted some more aroma)
Ferment with a clean ale yeast (US-05, 1056, 001)
I won't garantee it will turn out just like 420, but it should be a solid APA. Good luck.