Does anyone know how big of a sleeve you can install without having to bore the cases on a 350X? Or in other words, does anyone know the diameter of the cylinder opening in the case (one of my engines is together, and the one that is apart is being borrowed by a friend for a 250ex mock-up).

I'd like to try installing a sleeve for a 440 kit for a 400EX into one of my spare 350X cylinders. The OD of the 440 sleeve is 3.729" (94.7mm). The OD of a standard 400EX sleeve is 3.589" (91.2mm). I have no problem with boring the cases, and could easily do so myself; but if it doesn't require any lower end work I might just stick to the smaller bore. With stock stroke, the 440 sleeve would yield 423cc. My other plan is to graft on an entire 400EX top end, but that's going to get involved...