The Mazda 929 1" bore master cylinder fits, but it'll reduce clearance to the elbow more, I'm guessing, since it even makes it difficult to fit a CAI there on the FS.
The MX3 booster would probably just reduce the amount of vac assist, so the pedal would probably feel a little harder to press to get the same braking out of it, but it might be worth it, anyway. Since you're considering the Tilton three pedal assembly, ANY assist would be more than you have with the Tilton setup, despite not being as cool.

Then again, the 1" bore cylinder is the same deal, but man, it makes that pedal ROCK hard, which is awesome. =) You really feel everything through the brakes after that.