The rotary broach holder shouldn't be too hard to make, I've drawn up a page or two of ideas on it and have researched enough info on the web to know the critical dimensions I need. I found a quality 0.140" hex broach made by Slater on Ebay for about $25 a couple months ago, so I bought it with the intention of using it to create the internal hex in the boring head's leadscrew. With a bit of time setting up and the right tool steel, building any kind of simple geometric rotary broach should be fairly easy for use in the typical home shop. I'll try to cover those things when I get there; Dean Williams (see the link in the previous post) covers building this boring head and hosts the prints on his website, so I figured that anybody interested in building one of these could follow his footsteps. I don't have time to cover all the little details of this project anyway.
Here's some pics: