i've made an extract Celebration clone several times with very good results. I got the recipe from the BYO clone magazine... as best as I recall it is as follows:
5.5 lbs pale DME
2 lbs 2-row
1 lb Crystal 35
.5 lbs Carapils
Steep grains @154 for 45 minutes
1 oz chinook @ 60
1.5 oz Cascade @ 30
.5 oz Cascade @15
tsp Irish Moss @ 15
Dry hop with .66 oz of both cascade and Centennial
I noticed that both times I brewed this, the bitterness was there, but the hops flavor was not quite as prevelant as I had noticed in the real version. So, you might want to to delay the cascade hop additions to a little later in the boil or add some at flame out...
Hope this is helpful