Very Nice Job restoring your CB750A!!! I was just looking at a used 4-1 header like this at my friend Pat's cycle salvage, it was marked '70 CB750, but I figured it was an aftermarket one as I knew they didn't have a 4-1 in 1970 lol. Now, I am thinking someone took a 1976 CB750A header and installed it on a 1970 CB750K0, and that's how it was when it got parted out! If it fits a 1970, it should fit my 1971 CB750K1... The header part is in really good shape, and it has the finned collars like mine also. The slip on can, not too bad, but it has some rust and a few scratches. But, I can get it from him *cheap* as I do help him out a bit, and we are good friends!
He has a lot of CB750A parts, several engines, and several whole bikes in his warehouse. He has been parting bikes out for 30+ years!
I also saw a 1977 or 78 CB750 SuperSport (F2 I think) another shop owner I know got from an impound for $100... has a Windjammer on it and hard bags, and 22k miles on it. The bike looks pretty nice, but no title, and paper from the sheriff said it couldn't be titled... Oh well, I digress... Again, great job on your CB750A!!!
Charlie