Why not? Any computer program is just a very large number. Even thought the emacs build process that calculates the large number corresponding to the current version of emacs hadn't been performed in 1990, the number itself "existed" back then as the outcome of any number of other possible computations.

On the other hand, you might have problems with dll dependencies.

GCC stage1 is deliberately written in K&R C so that you can do this kind of bootstrapping. You need a few unix tools (e.g. make - but again, a version from 1990 should work, find yourself a solaris machine or something); I don't remember exactly what emacs depends on, but it should be fine. Getting a modern environment on old unix boxes (or under windows SUA, whose unix stuff is old enough that it comes with X11R5) is fun and usually requires a bit of fiddling but nothing too serious.