A dial-selective intercom is a nice thing to play with. Look on Ebay for "teltone C-19" or "teltone T-19" They mount outside the smaller KSU's, or inside the larger ones. They use the same power feeds that are already available in the KSU.
Yes, some people, not realizing how plentiful the flat fuses are, have used automotive-type in-line fuse holders. Just bridge across the fuse screws with the two leads. A short piece of one strand of copper from a stranded extension cord makes a nice fuse wire, in a pinch. They are called "no-blo" fuses for their robustness.
I have never needed to exercise any old electrolytic caps in telephone equipment. You could bring them up to full input voltage slowly (start at one/fourth voltage, say, and bring them up over a period of a day or two) with a variac, if you're concerned. All the components are easily accessed.
