Your goal in doing this is to gain 2MPG? Seriously? You could likely get through this and end up with the same MPG and a significantly lighter wallet. The carb is just one element of the tune. Changing out a carb isnt necessarily going to resolve your MPG issues. There is likely much more going in your situation than just a mis-tuned carb. You also need to focus on your ignition system (initial and total timing), timing curve, vacuum advance to start with.
To improve MPG on my old Pontiac I leave it in the garage and drive a vehicle that gets 20+ MPG..
Oh, and if you do decide to rebuild the Q-jet, take Rocky up on his offer. He invited me to his house ages ago and we put my distributor on his machine and curved it. Rocky is a super nice and very knowledgeable Pontiac guy.