From the pics you have, that bike is 1) not a racing bike; 2) Probably not a bike built by paul dunstall; and 3) definatly not a race bike, now anyway.
Dunstall made 2 honda models in 1973:
http://woodgate.org/dunstall/models+.htmlDunstall also made component parts and kits you could order out of a catalog. my 1976 cb750f has all of the dunstall parts you could order sans the tank and seat. What you have there is probably a bored out stock cb750 with a lot of dunstall pieces on it. Since dunstall stuff is high quality and very expensive these days the inflaited asking price is probably justified (if within reason, how much is it anyway?). If he doesn't have the accompanying paperwork then it probably is not a real dunstall. If this bike is in the US, the overbore kit could be an R/C engineering kit which would be big bucks today too. That header although nice looking des not look like the dunstall exhaust.
from this site:
http://woodgate.org/dunstall/ After 1966, your log book should refer to the machine as a Dunstall if it was built at the Dunstall factory. It is still worth checking the Norton factory records to confirm when the machine was shipped to the Dunstall factory. Even if your log book calls it a Norton, still check the Norton records as it is not unknown for the details to be wrong on the log book.
These comments only really apply to Norton based machines built in the U.K. If you are investigating a Norton based machine in another country then you may be reliant on the local vehicle registration documents to record the make correctly. Some machines were imported direct from the Dunstall shop and so would show as such in the U.K. records. Unfortuantely, before complete machines were exported to dealers, machines were built from kits supplied by the Dunstall organisation and fitted to existing machines.
For some of the major less common makes such as B.S.A, Yamaha, etc., then the job is a lot harder as the machines would have been sourced from another dealer. The original factory (B.S.A., etc) would not show any link to Paul Dunstall. You will have to rely on supporting documentation to prove the Dunstall link.
If the engine and frame numbers do not match, then it is still a Dunstall if the records, or your log book, show the frame being dispatched to Paul Dunstall. Having a Dunstall built engine in a factory built frame is unlikely, but not impossible.
