I am not sure how active Jef is. We must wait to see if/when he relaunches his site: http://abraxas.jefdeb.com/
The old site had lots of schematics and ideas so hopefully the new site will be equally useful.
An early version is sold in kit by a friend of Jef's. http://spudkit.com/
If you read through all the Hawthorne forums you'll also see modifications by Terry G to upgrade the kit.
Jef's builds do exceed the kit in every way. He went all out on mine, including screen regulation and the headphone adapter/output.