Uhm... monochrome CRTs don't have shadow masks so "dot pitch" is a non-sequitur. (And LCD panels produce grayscales in a completely different manner than CRTs.) The tubes in those nine inch mono VGA monitors are functionally identical to the one that shipped in a toaster Mac, and in fact there was a thread a while back where someone discovered the tube in a particular model that was all over eBay could actually be used as a compatible replacement. The only reason to swap the tube would be if the original had a bad case of phosphor burn (a distinct possibility, granted), but even then burn-in isn't going to affect the "number of grays" displayed, it's just going to contribute to an uneven brightness across the total picture.