I wouldn't even think of changing the grist - it has such a great malt profile. It would benefit from a bit more IBU's as well as slightly more hop flavor and aroma. Both scoresheets suggested increasing the bitterness - when I brew this next I plan to be around 30-32 IBUs with slightly more finishing hops (21g or so total in the 1 minute addition).
Style: Special/Best/Premium Bitter
Name: Bag End Bitter
Yeast: WLP002
Fermentation Temperature: 65F
Original Gravity: 1.043
Total IBU's: 26.5
Colour (EBC): 23.4 EBC (11.9 SRM)
Efficiency at End of Boil: 68%
Mash Length (mins): 90
Boil Length (mins): 60
Your Vessel Type (Pot/Keggle/Urn): Pot
Source/Credits: Basically a cross between Jamil's ordinary and special bitter, while using English Extra Dark Crystal instead of Crystal 120 and floor malted Marris Otter instead of basic UK Pale ale malt (the floor malted grain adds a little more maltiness and color I think). I also ferment colder (he recommends 68, I like WLP002 at 65).
Notes/Instructions/Comments: If you can get 002 fresh enough and you oxygenate, you can get away without a starter. If not, make an appropriate starter. Ferment at 65, I did a D rest after the krausen dropped (day 3-4) up to 69F at a rate of 1 degree F per day. Kegged at 14 days, was drinking at 16 days, luckily I had the sense to fill 4 bottles before the keg was kicked at about day 30 from brew day. This beer is excellent young.
Your Vessel Volume (L or gal): 15 gal
Your Vessel Diameter (cm or in): 16"
Water Required (L or gal): 8.44
Mash Temperature (C or F): 152F
Volume at End of Boil (L or gal): 6.25gal
Volume into Fermenter (L or gal): 5.25gal
Brew Length (L or gal): 5gal
Total Grain Bill (g or oz): 3,967g
Grains - Colours - Percentages and/or Weight (g or oz)
Grain 1: 3628g Floor Malted Maris Otter (4.5L - Warminster)
Grain 2: 226g English Extra Dark Crystal (150-160L - Simpson's)
Grain 3: 113g Special Roast (50L - Briess) - this may be hard to find overseas, here is a description in case you need to substitute it - "50° L. Contributes deep golden to brown color and toasty, biscuity, sour, and tangy flavors." I would probably just use another 113g of the English Extra Dark Crystal if I couldn't get Special Roast.
etc
Hops - AA% - IBUs - Weight (g or oz) at Minutes
Hop 1: EKG - 5% - 19.7 IBU - 28g @ 60min
Hop 2: EKG - 5% - 5.1 IBU - 14g @ 30min
Hop 3: EKG - 5% - 1.7 IBU - 14g @ 01min
Mineral: Water profile - Ca 114, Mg 24, Na 20, SO4 349, Cl 48
Finings: Whirlfloc - half tablet at 5 minutes
Keep the carbonation subdued, this can taste very harsh when overcarbed. I like mine around 1.5 volumes. It tastes like a completely different beer at 2.5 volumes (very harsh and gross).
Let me know if you have any questions. Here's a crappy cell phone pic:
