Pictures provided by French seller show the casting dates ARE 9-11, (September 11, 1969.)
As yet, there are no sandcast crank cases known to have been cast after September 1969. And, there is pictoral evidence pressure cast vins as high as 9xxx were manufactured September, 1969.
The 13xxx numbers, on the French bike, are a November production date.
Determining why the French sandcast cases are stamped with a 13xxx range pressure cast vin and in a 13xxx frame requires the same type of thinking as if you were riding your motorcycle and it unexpectedly died at the edge of the road. Would you pull the engine and do a major engine rebuild at the edge of the road -or- would you remove the fuel cap and peer in to the tank to see if the tank has gas in it ?
Assumptions remain. The 10-hole clutch cover with the 10th hole blanked off is a red herriing. It is, as yet, unknown if this cover is a Honda factory part or a dealer/owner modification.
Does not make sense why Honda would make a 10.h cover to fit a 9.h crankcase. Has this cover been with the sandcast engine from the time the engine was built new in 69 at the factory? Was the engine even built at the factory? Or, was the engine built from bare cases by the dealer or owner? It's hard to believe the 10.h cover with a blanked off 10th hole is a Honda factory part.
ASSUMPTIONS: (not absolute statements)
1. Well into the 10.h pressure cast crank case production run, for no apparent reason or because a set of pressure cast cases were defective, the Honda assembly line used a pair of 9.h sandcast cases and stamped the numbers to match the 13xxx frame. Honda modified or made a 10.h clutch cover to fit 9.h cases. (Never mind that the 10.h case was a design improvement and the pressure casting process was used to increase production output.) It's difficult to imagine Honda would have had an engine returned to Japan from France for replacement due to crankcase damage (this would be a dealer job) and then Honda Japan would replace the damaged 10.h pressure cast cases with 9.h sandcast cases. It is a little easier to imagine the engine was returned to Honda Japan from a French dealer because the dealer reported to Honda the engine as defective and needed returned to Japan for examination at the factory to authorize repair and then the factory proceeded with the repairs. This seems unlikely because WHY would the factory replace 10.h pressure cast cases with 9.h sandcast cases ? This logic does not fit well, if the scenario is carried out.
2. The riveted steering head vin tag indicates bike was exported from Japan to France and likely carried a set of a pressure cast 10.h cases. After retail puchase, the pressure cast cases suffered damage from chain failure. The owner of the damaged p.cast cases brought the bike to a French dealer for repair, the dealer had a set of sandcast cases in stock -or- the dealer ordered a set of replacement cases from Honda and the cases shipped from Honda were sandcast. This could be a reasonable assumption, the 10.h clutch cover that was on the damaged 10.h pressure cast cases was modified to fit the 9.h sandcast cases, likely by the dealer, (less unikely this modification was carried out by the owner.) Crankcase damage to thrown chains was a fairly common problem, the dealer could have had a set of sandcast cases in stock and did not have a replacement 10.h cover for the 9.h sandcast cases. Being still somewhat early into the pressure cast production, it is possible there were no pressure cast cases with blank vin pads yet available from Honda and since blank sandcast cases were available, sandcast cases were used. Finally, the dealer had a set of Honda stamps and stamped the number from the pressure cast cases into the sandcast replacements. Scenario #2 would seem more likely than #1.
Careful study of the pictures suggest the engine could have been out of the frame in the past. Careful study notes a RH front engine plain head hex mounting bolt to not have #8 markings on it, suggesting the engine could have been removed from the frame. It would be helpful to be able to do a physical inspection of the bike, to look for tell tale signs of engine removal or other changes made on the bike after it left the assembly line.
Careful study of the pictures reveals the bike has had some changes to it and is likely not 100% original nor correct
Just some fodder for continued discussion on this interesting machine.