You can easily cut a Scarf Joint, for your guitar necks, using a Radial Arm saw! The 1st step is, set your saw arm to cut at desired angle! ( usually 13-15 degs) next: using a straight piece of hardwood, set up a fence, 90 square to table fence, and at leading edge of saw blade path.
run your headstock thru planer to desired thickness. And, a couple passes of the newly angled joints over the belt sander... and, Viola!!! A Beautiful Scarf Joint!!!