Is this conversion right?

I'd like to convert Lil' Sparky's Nut Brown Ale from AG to PM. I'm pretty much going off a whim on how to do this, and plugged some numbers into Beer Smith. But would it be correct to cut the 9 lb of pale malt down to 2.5 lb, and then substitute with 4 lb. of Light or Amber DME? Plugging that into BS gave me the same OG of 1.057, so it seems correct.
Also, are the steps for the PM then the same, only cut down on the mash volume? That is to say 6.5 quarts at 165.9 for 60 min. And what about the sparge, do I need to cut down the volume on that as well?
Thanks as always!
EDIT: What type of DME should I use for this - Light, Amber, Dark? I would like light just basted on the rest of the bill, but I'm a noob.

beersmith should give ya all the qtys ya need. sparge volumes can only be viewed in the brewsheet pages

This article will tell you everything you need to know. It's great for converting AG to PM.

http://home.elp.rr.com/brewbeer/extract/pres.pdf