You can use any combination and amount of hops you like. It's your beer.
Totally agree with all Rob says - and if you really want to "clone" an American IPA then Fuggles aren't the way to go.
However, if you want something interesting, tasty - with American overtones, then yes, this sounds good. Cascade is a very different hop to Fuggles, so using the two together should give you a more complex and therefore subtle hoppy flavour and aroma.
I haven't used a Fuggles/Cascade combination but I have used Fuggles or Goldings in combination with Centennial, Motueka and Ahtanum, with very good results to my palate.
What I strongly suggest, though, is do not boil Fuggles for 60 mins! They contribute little bitterness, and afer 60 mins boil not much of their flavour or aroma will be left :-?
Cascade is a bit stronger on the bitterness front, but even then I wouldn't boil it for 60mins either. Basically, your suggested recipe would be putting 80g of hops in your boiler - and after 60mins you'll have moderate bittering, and nearly all the flavour and aroma will have gone.
My recommendation is to use a very high alpha-acid hop (which means a very bitter hop) for your long boil. I use Warrior (alpha-acid about 16 whereas Fuggles is about 4. Which means you only need one-quarter of the quantity of Warrior to give the same bitterness). Warrior is well known for providing bitterness without harsher flavours. There are others such as Magnum, or even Citra is pretty high alpha. You might only need 20g of Warrior for your 60min boil.
Otherwise, your dry-hop looks very good to me. This should give good aroma.
A personal suggestion: I'd do a 60 min boil with just high alpha hops.
Forget the 15min step (again just me...).
At flameout add your 75g Cacade & 75g Fuggles. (I'd leave them sitting in the hot wort for half an hour before cooling). Do you plan on cooling your wort, though? - I don't do this, but it seems most people do. If like me you don't actively cool, but let the temperature of the wort drop naturally, then I'd suggest cutting down your bittering hop to maybe 75%, because hops continue to add bitterness until the temperature falls well below boiling point.
Good luck with whatever you decide - but hell, most well-made beers taste really good!