Wit Graff

Looking to do something with a Wyeast 1762 Belgian Abbey II that I have propagated. Thinking of a wheat beer/cider graf with a partial mash that would end up with two gallons of cider in it. I am worried that it needs a bit more bitterness...not sure how many IBUs a typical witbier has in it. Another issue I have is what size boil to do. If I do a full five gallon boil I won't cook off enough to leave room for the cider. Here is what I have so far, any suggestions or comments are appreciated.
Thanks,
mfs

Wit Graf
16-E Belgian Specialty Ale

Ingredients:
Mash in:
.50 lb Honey Malt
1.0 lb Pilsner Malt
1.0 lb Torrified Wheat
1.0 lb Oats Flaked
3.0 lb Standard 6-Row
Boil:
4.0 lb Dry Wheat
3.0 lb CBW® Golden Light Powder (Dry Malt Extract)
1.0 ea WYeast 1762 Belgian Abbey II
1.0 oz Hallertau Mittelfruh (4.5%) - added during boil, boiled 60 min
1.0 oz Hersbrucker (2.4%) - added during boil, boiled 5 min
16.0 lb Ziegler's Cider
1.0 tsp Irish Moss - added during boil, boiled 15.0 min

Wits are generally in the low to mid teens for IBUs (not many have hop aroma), although for such a strong beer I'd up it. Boil with 2 gallons less water than you usually would to leave room for the cider.

Also you seem to be looking at a ~1.117 OG with 70% efficiency, about 2.5X stronger than a regular wit (just making sure that is what you are going for).