Thicknessing the headstock....

On a tele, the headstock is about 19/32". The back of the head is level with the heel of the neck. I marked it up on the bandsaw. Using a fence, I cut just shy of the transition area that extends to the nut. I'll sand the last bit. It's important not to cut too far - so you can achieve a natural curve from the headstock face toward the nut.

Rough cutting the fret slots....

I cleaned the dust out of the fret slots (or what was left of them!) with a piece of sand paper. Then I used my fret saw to extend and deepen them. I'm not going to do the final sawing until just prior to fret pressing....

Getting there...

You can see here how the fret slots have almost been obliterated.... this turned out to be a good measure of how even my sanding was (at least in 2 dimensions) and kept me on track. You can see here how thin the fingerboard has become.... I did move up to about 180 grit towards the end. I was measuring the thickness constantly with vernier calipers.
Be sure t measure at several points along the neck. I was going for a 1" thickness. Bear in mind the dot inlays have not been placed and nor has the back been shaped. Both of these will at least remove a fraction more wood...

Thinning the Fingerboard...

I took a 12" radius sanding block, used 100 grit paper and got moving.... worked up a bit of a sweat here. After 25 years of playing rosewood fingerboards, I realized why it's called ROSEwood... the dust is truly rose. You get covered in it! and it has a divine woody, tropical smell...

Trimming the Fingerboard

This is pretty straightforward.... just be careful on the band saw not to cut into the neck ;) .... keep it a close cut, though! Once trimmed, I gave it a light sand - but really cleaned it up later on.... Notice how thick the fingerboard is.... I don't know why, but thick rosewood boards bug me.... must thin it down....

Fingerboard in attached!

Here's the glued fingerboard. ready for trimming....

Attaching the Fingerboard....

It's a good idea to score the underside of the fingerboard to help the glue.
Cover the truss rod cavity with masking tape, and trim the tape close to the cavity. Spread your glue (I used Titebond) with a credit card or similar plastic.
Remove the tape!
I had marked the center line of the fingerboard, so I could line it up directly on the neck.
The important part is to be straight! The face of the nut slot should be 18 7/16” (18.4375”) from the edge of the heel (thanks Jim...).