Not really sure, I suspect the above replies are accurate. I never really cared
That one underneath you may not have room to mount other caps safely on the bottom. Might have to fire up the compressor and buzz it off with a cutoff wheel, then feed the new cap terminals through the bottom, from the top side. At least that's the way I would do it....but I don't care about making everything under the chassis look like it did 60 years ago, I just want it to work right. Everyone's got their own approach.
I know the cap you're talking about, and it's probably got a phenolic base, which is really brittle and will crumble if you're too rough in trying to get it apart.