There used to be a utility called Test Pattern Generator that had some great patterns built in. However, a ruler in MacDraw works well too if you're looking for accuracy of inches.

One of the tools I use with CRTs is a soft measuring tape. If you've ever been to a tailor, you've probably seen one of these--he will use it to measure waist size, hem length, etc. These work well on any screen not only to check size accuracy, but also to center the screen with the yoke, as the straightness of the black border can be examined closely with the tape next to it.

A lot of people actually did stretch out their screens at some point to use the entire viewable area. Most did not, however, and finding a Mac with the exact specifications really isn't that hard provided its power supply has remained sound.