Ok here's the grain bill I came up with.
Volume: 5.5 gal
Color: 8.5 SRM
12.00 lbs Maris Otter (this is my guess as I highly doubt they use Pilsner malt in this beer)
10.00 oz Crystal 40L
8.00 oz Torrified wheat
4.00 oz Aromatic Malt
As for the bitterness, I thought this beer was really complex so it's difficult to say how bitter it really was. It's probably a combination of the grain bill, the fermentation profile (ie yeast used and fermentation temperature) and also the profile of the water they used. I'd say it's a fairly bitter beer but that could also be due to high sulfate water which would increase perceived bitterness. As a first attempt, I'd probably target about 45 IBUs and then adjust bitterness on a subsequent batch. I think at 45 you'd still get a pretty decent beer if it ends up off the mark.
1.20 oz Challenger (7.5%) at 60 min (~38 IBU)
0.25 oz Styrian Golding (5.3%) at 15 min (~1.5 IBU)
0.50 oz Challenger (7.5%) at 15 min (~4.2 IBU)
0.50 oz Fuggles (4.3%) at 5 min (~1.9 IBU)
Again, no idea if this is the actual recipe, but I think this would turn into a good beer even so. If you decide on brewing this and do a side by side comparison, let us know how close it is to the real thing. Good luck!