For obtaining XFree86/OS2 see the XFree86 for OS/2 homepage, on installing and for further details on Lesstif, see the Lesstif for XFree86/OS2 description by Michael Holzapfel.
The original XEphem package is offered in two versions: First as a whole package for those who download it on the computer where to install it (xephem31.zip), and second partitioned in two files matching 1.4-Mb floppies (xephem31a.zip and xephem31b.zip).