Have you compared the engine serial number to the frame number to see if they match? I ask because your pics show an earlier cam chain tensioner assembly installed. That could mean several things - the tensioner was swapped, or the cylinder block was swapped, or the entire engine was swapped. The tensioner on there is from a '75 or older engine .....
..... and as you can see in your 2nd pic, your later linked carb set barely fits above it. In fact, the angle bracket connecting the carbs may be resting right on the adjuster cover nut. For linked carb set clearance, the later tensioners used a smaller, shorter cover nut and were angled down slightly.
Very keen eye, the previous owner did say the tensioner was swapped by his previous owner. I am hoping to change it back to the correct type, seeing as I am changing the block anyway for one of the 750cc kits from mike.