I usually try to keep 2 lbs of the base malt for the mash, then convert the rest to extract. In your recipe though, that would be 6 lbs of grain. I can only do about 5 lbs so I'd probably do:
3 lbs light LME or 2.5 lbs light DME
1.5 lbs 2-row
2.5 lbs Crystal 40L
.5 lbs flaked oats
.5 lbs Special roast
That would give me a 5 lb mash and still should be enough 2-row to convert the oats and special roast (the Crystal doesn't need the enzymes). Extract is always a little darker than 2-row so I don't think you'll miss the other .5lb of crystal.
I had found a great article on converting AG to partial mash, it doesn't seem to be on the net any more but I have a copy of it on my work computer, if you want to PM me your email address I can send it to you on Monday.