I'm in the process of finishing a big headstock modern construction neck with Tru-Oil right now; reglar ole maple with a Pau Ferro fretboard.
Personally, I feel it's much easier to finish it while separate from the guitar. Just tape off the fretboard and the parts of the neck where it fits into the body that you don't want finish on first. It just seems like it might be tough to keep from getting the oil on a part of your guitar where you may not want any if you assemble it. And the neck by itself is pretty easy to deal with as far as applying the oil and hanging to dry.
You didn't ask, but I might give a little bit of advice about applying the finish. Apply VERY LIGHT coats. On the headstock, I only put 2 small drops on each side, and spread those around. I use essentially one smallish drop to go around the sides of the headstock. I put only 3 VERY LIGHT coats on the back of the neck, let it dry for a few days, and scuffed the back down with gray (extra fine?) ScotchBrite. I want a semi-glossy finish on the headstock, so I'm applying only a few more VERY LIGHT coats. I will scuff the headstock with that gray ScotchBrite before my last coat, and put a some thinned out Tru-Oil on for the last coat. After a week or so, I'll scuff it lightly again, then buff/rub it.
When you apply a VERY LIGHT layer/coat, if you discover you've missed a small area, let it dry and THEN get it with your next coat. It doesn't really work out to try to smear it around after the stuff has dried for 5-10 minutes. Doing this job where there's plenty of light will help a lot with seeing where you've applied the finish, and where you haven't, especially after your first coat. It just gets harder to see where you've applied it after there's a layer or two already on. At least it is for old blind bastards like me...... :icon_scratch:
If it matters, I've began using the green latex or vinyl gloves on my hand, and applying the oil with Mr. Pointy finger. For me, this works well; better than anything else I tried. I either got bubbles and "brush marks" with any of the numerous "tampons" I tried to put down the oil with, or they left bits of fiber or paper fuzz in my newly laid down finish. I tried old t-shirt material cut into about 4" squares. I put either more t-shirt material or a cut up blue paper shop towel inside that, and made a little applicator like shown in a few videos I watched. Like I said, it all either left "streaks" that needed level sanding more often, of bits of fibers. I also tried (without much success) medical cotton gauze pads, cut up squares of either blue paper shop towels or cotton t-shirts all by themselves, and wasn't happy with those. This was just my own experience; hopefully however you choose to do will work out just wonderfully. I chose to give it The Finger. :headbang:
Here where I live in western Oregon, it's cooled off dramatically at nights lately, and only getting into the low-to-mid 60s for daytime high temps. Dunno what the humidity is, but I know the coats I put on dry slowly now. So I put a coat on in the morning, let it dry, and maybe will put on another one in the evening. If you live in, say, a place like SoCal or AZ, you can probably put on 3-4 coats a day. Or, you may need to only put one on and let it dry for 24 hours. Just depends on the climate of where ya live. When you level sand it, if little "rolls" of finish come off on the sandpaper or lays on the body in little soft "clumps", you haven't let it dry enough. Stop, let it dry some more, then go back to sanding and recoating. It needs to be dry to work with, and when you apply your next coat. Not waiting long enough can make a finish on a guitar that may take months or a year to completely cure. This again is another reason for VERY LIGHT coats. They simply cure faster.
Lots and lots of time, and lots and lots of patience will be your new best friends when finishing a guitar. :icon_thumright:
Hope this helps you, or someone. If you knew all this already, I apologize. Just trying to help.....