Marty,

Are you actually restoring an original Ki-27 trainer/fighter or is it a replica? Either way, that's very cool! I think the allies called it the "Nate".

They were built by the famous Nakajima Co. as well as the Mansyu Co. Both still exist with Nakajima having an office in LA. They are now manufacturers of plush toys and collectibles--quite the sea-change from famous aircraft producer. Mansyu is now a food processing co. in Japan. You should contact each to find out if any archives exist of their original manufacturing companies. You never know what you may discover by taking that first step and what it might lead to. You could also contact the Smithsonian, they have an incredible array of archival material.