The two steel bars and allen bolts hold the file securely and double as hand-holds. It's a little hard to see in these shots, but the surface the file is on is at about a 35-degree angle to the wide face of the block. The wood rests on the surface of the frets and the file trims the corners, with the result being consistently beveled fret ends which need minimal individual attention. I used the same procedure on my guitar and it worked nicely.
Most of the carving on the back of the neck is done as well, currently it's got a fairly wide, flat back. I've left enough wood that I can still go the trapezoidal route, but I might just thin the sides a little more and go for rounded.
The neck block is now gluing up to the back of the neck, it's an 1/8" of bubinga sandwiched between the neck laminate and a chunk of the same walnut the back of the body is made from.
Once that dries, I'll plane the added blocks flush with the neck laminate and glue the purpleheart rails on to the side, then time for pickup and bridge routing.