Here is a collection of PDF manuals, various mods, both military and civilian, and a collection of e-mail archives on the Hammarlund SP-600, both -JX and VLF-31 versions.
1) SP-600 Maintenance Manual
2) SP-600 Overhaul Manual
3) SP-600 Parts Manual
4) SP-600 Service Manual
5) SP-600 VLF-31 Manual
More later...