The Fonts (Removed) folder contains a time-stamped folder containing the fonts that macOS Catalina moved from my Mac’s Library/Fonts/ folder. A similar folder was created in each user’s. System fonts Avoid if you can, choose wisely if you can’t. System fonts are the fonts already installed on your computer. Some are better than others. In printed documents they present three problems. Many system fonts aren’t good.The Windows and Mac OS libraries have improved, but they’re still minefields of awful fonts.
My question: Is it 'safe' to install these fonts on my 10.6.4 machine?
Yes.
Or could the ancient fonts cause some kind of operating system meltdown or panic or whatever?
Only if they conflict with other fonts, or are corrupt.
Perhaps the OS 8 & OS 9 fonts are safe, but not the System 6 and System 7 fonts?
Anything from System 8 forward will work. System 6 used bitmapped fonts. These are not supported in OS X. System 7 and 7.5 though were a mix. There were both TrueType and bitmapped fonts. Only the TrueType fonts can be used.
It does depend on where you're reading about these old fonts. One site notes that TrueType fonts were introduced in System 7. Another states that there were TrueType fonts in System 6.
And even if they are safe to install: Will they work?
Yes. I have tons of old fonts; Mac TrueType from OS 9 and earlier, Type 1 PS fonts from way back, etc. They all work just fine.
What's the best way to install them?
The best way actually, with Font Book, is to
not install them. Which I will explain per the next part:
'Font Book' window pops up with an optional 'Install Font' button at the lower right. By clicking that button, does Font Book physically move the font file to the proper place in the OSX system?
If you look in Font Book's preferences, fonts you 'install' can go to either the /Library/Fonts/ folder, or by default, the Fonts folder in your user account. What you really want to do is activate fonts 'in place', which is to activate them from where they are instead of creating copies. Do this by creating a Library Set in Font Book rather than a normal set. Fonts added to a Library Set are activated in place.