Help with malt substitution for 90 Min IPA recipe

Hello everyone --
I'm looking for some advice on how to keep the malt profile of a recipe as close as possible while changing either the base malt, a specialty malt, or both. My next brew is going to be an attempt at DFH's 90 Minute IPA. I've only found one recipe online (it comes up everywhere, though), and it looks pretty good:
90 minute IPA Clone - Realbeer.com Beer Community

I have the hops ready to go (amazingly!), but not the right grains (recipe calls for 16.5 lb pilsner and 1.66 lb amber malt). I am putting together an order from B3 right now, but would prefer to make the beer sooner than I would receive it, using what I have on hand. LHBS is a $100 round trip ferry ride (and then 2 hours in the car) away (I live on an island), so that's not happening.

On hand:
15.25 lb Maris Otter
13.5 lb pilsner
2 lb light munich
9 oz aromatic
4 lb melanoidin
scraps of misc crystal (7oz 40deg; 3oz 60deg; 3 oz 75deg; 4oz caravienne; 6oz special B)

Under normal conditions, I am very much the RDW type when it comes to following recipes: I just want good beer. I would go with 15 lbs MO, 1.5 Pils, and cobble together the 1.66 lbs from munich, aromatic, and melanoidin. However. . . this is the very first time I have gotten a specific request from the wife for a beer clone, so I'd really like to get this thing right. (We recently went to the beer summit in Boston, and the 90 minute IPA was far and away her favorite.)

So, the questions:

1. Should I wing it with what I have? How much of a difference would it make, given that the flavor of this beer is so hop dominated? Should I just buy the wife a pound of amarillo for use on salads?

2. I can get the pils from B3, but not the amber malt (35 deg) called for in the recipe. B3 has something called brown malt, which sounds similarly english-ish, but is 60-70 deg. It seems like 1.66 lbs of that would be excessive. Should I order the brown malt, but use less? Maybe something like victory is closer?

3. If I go with the Maris Otter in place of some or most of the pilsner, how should I change the recipe to keep the malt profile the same? In general, I'm unclear how MO compares to Pilsner. Both are described as giving a better malt flavor than regular 2-row; however, one is lighter in color than regular 2-row while the other is darker. Since the amber malt (or whatever I sub for it) is intended to boost the maltiness of the beer, would I increase or decrease this when subbing in MO for pilsner?

4. My yeast will be a little different from the recipe (1099). I'm creating a big yeast cake of S-04 with an English pale ale right now; the plan is to toss the 90 min IPA onto it when the pale ale is done. Allegedly, S-04 is the 1098 strain, which should give about the same flavors as 1099, but with higher attenuation. Should I do something to try to correct for the dryer nature of my yeast? Up the mash temperature, or add some crystal? Or is the difference small enough that I'd come closer to the recipe by not messing with it?

5. Is the extreme verbosity of this post annoying or helpful?

thanks in advance!

You can use C20L, but here's a guide to making amber from 2-row.

Roasting Malt

That's a pretty cool article - I've always liked the process of home-toasting malt, so I'll definitely try making some amber some time.

I'm worried about the inconsistency in the product in this case though, since it's such a large part of the grain bill. Do you think I'd come closer by making 1.66 lbs of amber myself, given the natural variability in what might come out, or by substituting something else commercially made?