I've done 2 batches of this, the first last year and another this year.
The 5/4 is reference to instrument sizes, more specifically tubas inmy case. Normal size is 4/4, which is my regular dry stout. As far as tubas go there are some 5/4 and 6/4 instruments, mainly for large orchestras, so my bigger American Stout is th 5/4 and my Imperial Stout is 6/4.
The last time I brewed it I was out of Centennial hops so I used a total of 1 oz at 10 minutes with half Nugget and the rest split between Summit and Mt. Hood. It definitely wasn't Centennial, but wasn't off-base either.
That time I brewed it also came out a little drier, so the roast and bitter was a little more pronounced.
Brewsmith, I had no idea there were fellow tuba players on HBT! While looking for an idea for an oak aged stout I'm planning for January, I saw this and thought of the Willson 3050. Little did I know it actually was in reference to tubas. I know it's a bit late, but congrats on the awards! I'll be sure to shamelessly take many lessons from this recipe!
Thanks for the comments. I still brew that beer regularly, especially at competition time. It's getting brewed again in the spring before the National Comp.