I happened upon an old stack of slides, probably from the Mid-199's I suspect, that recorded the step-by-step transformation of a Breyer Stock Horse Mare into a Standing Stock Horse. This is pure Old School; before heat guns, before Apoxie Sculpt, before Mohair and before I had an airbrush! But the basics still hold true. Enjoy!
Mane
For the mane I'd run a bead of Elmer's glue along the crest, and glue down tufts of Fun Fur, pretty much the same way I do it nowadays (with mohair instead)