Extra Special Bitter, Help With Recipe!

I am waiting to free up a carboy, then jumping into a suggested recipe from BYO. Its an Extra Special Bitter, it goes as follows:

10.75 lb.(4.9 kg) Crisp Pale Ale Malt or similar British pale ale malt.
0.5 lb. (227 g) Great Western Crystal malt 15 L
0.25 lb (113 g) Great Western Crystal malt 120 L
8.5 AAU East Kent Goldings hops (1.7 oz./48g) at 5% alpha acids) (60 min.)
5 AAU East Kent Goldings hops (1.0 oz/28g at 5% alpha acids)(0 min.)
Wyeast 1968 (London ESB Ale) yeast

Transferred into a PM

7 lb (3.18 kg) John Bull Marris Otter or Edme Maris Otter English pale Liquid malt Extract.
0.5 lb. (227 g) Great Western Crystal malt 15 L
0.25 lb (113 g) Great Western Crystal malt 120 L
8.5 AAU East Kent Goldings hops (1.7 oz./48g) at 5% alpha acids) (60 min.)
5 AAU East Kent Goldings hops (1.0 oz/28g at 5% alpha acids)(0 min.)
Wyeast 1968 (London ESB Ale) yeast

Now, for my question. I only have normal 2-row LME, But I have a hell of a lot of Maris Otter in my stash. How much Maris Otter should I steep into my brewpot with my Crystal Malt?

Please Help me I have been tossing and turning in bed for the last couple of nights thinking of what to do!!
Thanks in advance
-Scott

If you're just steeping the crystal (not a PM) then none. There is nothing in the crystal to convert