Are we talking Tiger Cat? If so, the consensus with the X model is that the more weight out back the better. I'm not sure about the CC model.
Edit: I got my Xs and Fs backwards. The X is the CC. Insert F where I said X in my 1st comment.
The Grady White 26' Tigercat has a maximum horsepower rating of 400 hp, so you won't have an issue in regards to the maximum horsepower and a quick Google search shows a couple of guys that have put F200's or greater on their boats. If you're referring to a GW 263 Chase, then that boat has a maximum horsepower rating of 500 hp, so that shouldn't be an issue either. Not sure exactly what year you're referring to here, but I'm getting those figures from the 2000 GW brochure on their website. The first YouTube link below has a 26' Tigercat with twin F225's on it, and the second has twin 250 ETEC's on it. I'm thinking if they were able to do it, then you shouldn't have any problem in doing so either.