The plans headrests are possibly adequate seeing as they come directly from the Long-Ez plans, but then Burt has since added a complete roll over structure to his safety notes for the Ez. The cone head headrests may have looked good and been appropriate for the design of the Long-Ez but did not suit our tastes as a pair in our Cozy.

We decided the solution was to not use the plans headrests at all and go with something like John Slade's Saab Turbo 9000 ones or something like that. 
For rollover protection we would add that to our turtleback structure. The added benefit would be more visibility and less claustrophobia in the back seat.
For John the solution was as simple as cannibalizing his Saab, for us it meant two days on the phone to import junk, uh "salvage" yards trying to find one. We finally found joy in New Hampshire at $35 the pair Woo Hoo! leather even.. Chrissi liked that. Mounting was easy, tape up the headrest shafts and glass in place, remove the headrests.

Randi had a beef with the shoulder harness anchoring just being bolted to the top of the shoulder support "it looks like an afterthought.. a dune buggy or something" Of all the things we have done, none has added as much time weight and needless complexity as we spent reinventing the anchors to hide them in pockets in the shoulder support. We have not dremeled out the glass that is over the pockets yet because we are going to put a wrap of glass over the whole thing from the seatback front to back per plans.

 I will say this in our defense, if you want something custom, quality with a difference or whatever, it comes with a price. If you want a show quality finish, then expect to put four times as much work into it to achieve ten percent better results. Only you can say if it is worth it for you, just do not let anyone else be the judge if that is worthwhile doing.
If I were to approach this again in the future I would just make the seat upholstery go over the shoulder rest and cover the anchor points.