Office 97 can be installed on 64 bit windows 10 with original installer. I have done it just last month and it runs without any problems... and it is fast.
There are special workarounds, many of the old installers run a small piece of 16 bit code which doesn’t work in 64 bit Windows but because it’s so common Windows just runs a replacement version.
Failed the last time I tried, which must have been on 7. Will be a strong example for Microsoft dedicating resources to compatibility if they added it for 10 or with a patch update. (both their resources and the users', there's a crazy amount of checking for necessary compatibility hacks going on whenever an executable is started)