Detroit Iron - http://www.detroitironis.com/
- has been around for quite a while with, in this case, a Chevrolet parts book. It isn't searchable and uses Paperviewer instead of PDF but at least it's broken down into GM groups. You just have to know what GM calls parts and what group (0.000 - 15.000) they are in. I think they are available here on the TC Store as well. Hope this link works.
I have 3 years, 66, 67 and 69, and all have the same parts book - dated 1972, same as my paper copy - and listed as CHEVROLET PARTS 1964. Depending on the year you order for there are other manuals on the CD as well but they're pretty much useless. The 67 year is what I use most of the time and it has 1967 CHASSIS (mainly lubrication points), 1967 OVERHAUL (air conditioning compressor), and 1967 FISHER BODY SERVICE manual.
I'm not sure it's truly 'legal' since it's probably photocopied from a paper book that is copyrighted. I would assume Detroit Iron has permission to do just that since all the 'pages' in it are scanned (and not searchable)but they've had them out for quite a long time. Problem with the searchability is it's probably scanned images (then combined into a PDF format) and you can't search a scanned image for text. One would have to manually type in all the data (as text) then save that as a PDF file.
Another matter is what is in the Chevrolet parts book are quite often service replacement parts and may not be the same part number as the original. That and parts are superceded all the time changing the serviceable part number. All in all, they seem to be pretty good - again, if you know what GM calls things.