Marcello, a great piece of investigative research on your part !
Perhaps you have unearthed another question for which there is no definite answer !?
i can only tell you what i know:
1. the 69.4 parts manual calls for Stanley headlight; pn "33321-505-003 unit, sealed beam (Stanley)" (we know what we have found in literature does not match what we find on actual motorcycle.)
2. the 69.5 and 69.7 owner's manuals call for Koito headlight.
3. the Stanley logo in center of headlight glass is a circle. The Koito logo is semi-rectangular.
4. researching all pictures from original factory literature and magazines of the period, every headlight i could discern a logo - appears semi-rectangular.... Koito !?!
5. K1 and earlier original appearing machines i have found only Stanley lamps, no Koito. K2-later machines, i have found only Koito.
6. i believe (and please prove me to be wrong!) the concensus with restorers is; Stanley was the headlight machines came with from factory. (for what it's worth, i have a picture (Jan.2004 Motorcyclist) of a Vic World CB750 who's headlight lens has a round logo, suggesting a Stanley headlight in place.)
i believe the common assumption amongst restorers is; machines came with Stanley headlights. However, the above evidence suggests machines may and may not have come with a Stanley. At this time, it appears, there is more evidence to support machines were fitted with Koito.
What we do know, is many parts we see fitted to sandcast are not exactly like what is depicted in pictures. However, looking at my original literature, i see only a semi-rectangular logo on the headlight lens.
Given what we think we know, i would say, at this point, Koito or Stanley; either is correct.
Again, Marcello, great job of finding a topic for debate !
ps - another for what it's worth....... i have Stanley's in 4363 and 232. 2157 i have fitted with a period aftermarket French "Auteroche" H4 halogen unit. (my original cue, believing Stanley the correct headlight, came from 69.4 parts book and Wyatt, "Original Honda CB750.")
and finally.... the Feb.71, 1st ed. K1 parts manual calls for same pn 33321-505-003, as 69.4 manual, but does not include "(Stanley)" as noted in 69.4 book.
the Jan.74 1st ed. K4 manual calls for, "33100-300-673, not available, use 33100-341-701." (two completely different pn's from 69.4 and 71.2 parts books !)
SAE 6012, i believe, is an automotive spec headlight.
if anyone knows the differences between these pn's please speak up !