From the looks of it your gun started out as a rifle made at the Koishikawa Arsenal around 1933 or so. It appears to have been cut down to carbine length at some point as the upper band and rear sight are from a rifle, or else judging by the wrench marks on the barrel it's a put together using rifle and carbine parts. To my knowledge all carbines made by Koishikawa Arsenal were 6 digit s/n's. The #238 on the trigger and the bottom of the receiver is an assembly number,don't know about the ''35''it does't seem to be of Japanese origin. There's a lot of markings on the knox form I've never seen on an Arisakabefore, Russian
maybe? Someone wot knows more than me will be alone shortly and shed some more light on them, just hang on.