GB, I think it's a great idea but a huge amount of work in order to achieve the right result. To 'spread the load', some of our more prolific contributors might be prepared to put forward articles (based for example on some of the longer posts) on specific topics. I'm thinking of a 'bottom end', article, or chapter maybe. Also 'magneto' or perhaps ignition in general, wiring, frame, suspension, stripping for refinishing etc. All those aspects that chew up time when you first get your bike, or try your first bit of restoration.
A good place to start would be the basic structure, or contents list.
The 'guide' could, as you suggest, evolve as the forum's own Wiki.
Plagiarising content from other places would need control, to avoid copyright issues, with necessary permissions being obtained.
Interested to see if a volunteer steps forward!