I'm starting to get into guitar building soon. I took suggestions from some of the members here and bought 2 books on building guitars.
"Make Your Own Electric Guitar" by Hiscock
"Build Your Own Electric Guitar" by Oakham.
Hiscock covered neckthrough design in his 3rd guitar building example. Oakham also covered a little on that also.
If you're looking for free info, I've already seen several tutorials on building neckthrough guitars on the internet. Sorry, I don't have a link, but you should be able to google it.