Well, I’m gonna try to formulate a recipe here for PtE based on this recipe:
http://wiki.homebrewersassociation.org/PlinyTheElderCloneImperialIPA
Here’s what I just made:
Probably way off but my first attempt.
Note, I want to use the new Marris Otter Extract from Northern Brewer for the second listing of the Pilsen extract, it’s just not in the Hopville database yet.
It has the same ratio roughly as the AG recipe I based it off, with 45% pale and 39% M.O.
Theres a PDF of the real McCoy floating around on the web as well as the recipe Vinnie posted in the July/August 2009 issue of Zymurgy (including an extract version).
256 IBUs?
Actually it looks pretty darn tasty but I’m wondering about the IBUs being that high. Not that they can’t be that high, I tried the mikkeller 1000 IBU beer and it was quite tasty.
Note that I haven’t actually looked up PtE to see how bitter it is though. I’m having a southern tier jahva and thus I’m too lazy that gives me a good excuse. 
Also, general question for all…
OP’s recipe shows “tinseth” IBU scale. Beersmith has multiple scales. Is tinseth the one that everyone typically uses on beersmith/hopville etc?
FWIW I’ve had beersmith II set to tinseth.
Also your recipe says 6.9% ABV. I’m sure pliny is high than that. NOT that you should make changes based on this observation. Just sayin’ you might want to get feedback on that aspect as well.