Thanks for posting that link Jeff!
I too get about 50 - 55% yield on pulled pork, so if you want to serve every one the same weight for each meat, 3 servings / lb or 5.33 Oz / serving is good place to start for a single meat, if you want to pull it back a little with the two meats you could, but I wouldn't.
200 x 5.33 Oz = 1066 Oz or about 67 lbs cooked weight.
67 x 2 (or divide by 0.5) = 134 lb uncooked weight on the pork.
134 / 7.5 lbs = about 18 butts at 7.5 lbs each butt.
You don't loose more than about 10% weight off the sausage normally, so 200 x 5.33 = 1066 Oz or 67 lb of sausage or about 20 x 3.5 lb packs of sausage.
Though some folks don't go for sausage, if you're buying it by the weight you could go for the full 67 lbs, but if you're buying it by the link, and they weigh in at 3 + Oz / link you could get away with 200 links, which is only about 17 packs instead of 20.
Disclaimer: This is just my opinion, I don't cater bbq at the moment.