I had the same problem with my 59. I took it up to 11s with a wound 3rd, and the 6th string would not intone correctly.
Turns out that the bridge screws are actually a standard electronics thread -- 10-40, I think. I found them at Radio Shack. A pack of assorted lengths was about $3.50. The ones I got have Phillips heads instead of Allen. Frys, Micro Center, etc. should have them.
The longer screws stick out the back of the bridge a bit; but as long as the intonation is right I don't care about stuff like that.
When you take out the old hex screws, you'll see that they're pointy on the end. That's because inside the bridge, the screws press against a disc that has a V-groove cut into it. If you put an unmodified machine screw in there, the v-groove will trash the threads on the end, and you'll never get it out again.
I used a Dremel tool to grind the tips of my new screws down to a point that would fit into the v-groove. Make sure you secure the screws really well in a vise or with some vise-grip pliers when you're grinding them, and don't run the Dremel at too high of a speed. You could probably use a file if you don't have a Dremel.
It sounds harder than it is.
I play mostly rhythm on my 59, and I think it sounds and plays much better with the heavier strings. I did have to tweak the pole pieces on the mags to balance the string volume for 11s. The Tyler mags sound so good now that I use them more than the modeled tones.