In theory a few parts changes should allow you to alter any common "PC" monitor to handle the NTSC and PAL frequencies of the Amiga. The question is, which parts? It's a damn shame that except for TIMM, the companies making monitors decided it wasn't in their interest to make monitors that scanned at other rates. If they did you'd use them for TV's, and with DVD and VHS players.
They would much rather sell you two CRTs instead of one.
{bleep}s. We have much to thank Commodore for.