Mark, these are good questions. i would not say they are stupid. Probably some research into the manufacturing history of these Dunlop and Bridgestone tire companies would be helpful. what i remember when i got back from my trip to California early June 1970, the tire and chain were both gone; the dealer did not have the chain or tire designed for the 750 and he told me he could not sell me a tire or chain that the factory did not recommend. as i recall i had roughly 4,000 miles on the odometer. i have NO idea what tire was on 4779 from factory new; what i do know is a tire specific for the CB750 was unavailable in California (the dealer at Vallejo told me he had no tire (or chain) for the CB750 and therefore to not ride high speeds on the way home from California to Nebraska.)
Sometime around the time the CB750 was to begin production, the factory had their undies in a wad with the motorcycle manufacturing section of Bridgestone; it is fact that Honda told Bridgestone they'd quit buying tires if Bridgestone didn't quit making motorcycles. my understanding is the Honda factory had the chain and rear tire manufactured to spec to meet the until then unheard of performance the CB750 was capable of. and i have that memory of Art Olsen at Olsen Brothers Honda/Triumph, Sioux City, Iowa telling me i would have to wait for a chain and a tire for 4779; given Art saying i would have to wait for a tire and chain tells me that tires and chains fitted to Trident's were not suitable for the CB750. (Art had Trident's on the showroom floor and if i recall correctly both Trident's and Rocket III's were fitted with K70 front and K81 rear. the K81, if i understand correctly, was designed specifically for the Commando and the triples...)
maybe asking other questions such as the following could shed some light on if Superspeeds were on early sandcast vins... "What evidence exists that Superspeeds were fitted to early vin sandcasts? "What dates did these special Dunlops and Bridgestone tires first become available?" "Was the relationship between the two factories (Bridgestone motorcycles) so strained that Honda was not at the time purchasing tires from Bridgestone?" "Did demand for the Superspeed exceed supply?" -or- "Was Bridgestone even fully tooled up to begin production of Superspeeds prior to or very early during CB750 production?"
Mark, your questions are on target. if i understand correctly i think your question is, "Were Superspeeds were fitted to the very early CB750 sandcast vins?" Another question could be "What is the earliest sandcast vin that a Superspeed tire is found on a sandcast vin?" However, finding answers to other questions such as i pose might answer your primary question.