I have two June K code convertibles, less than 100 units apart. Bolts heads on the inside of the engine compartment on one, heads in the fender well on the other. Also interesting is that the fender top bolts on one use star washer, on the other disk washer.
That would be very unusual for a San Jose built car IMHO given the great numbers of examples available on San Jose cars. Would IMHO suggest (seen it before) that the bolts were removed and replaced in a different direction when reinstalled. That use to often be seen on restored cars where they were built in a different part of the country and copied unrestored cars built at another (more local to the builders) plant.
Does this happen to be on the same car and the same side as the fender with the later raised triangle reliefs in the fender on a 64 built car? As you mentioned in another post.
Could have even explained the replacement of one or more of the bolts. Suggest that looking at other cars built at the same time might provide some addition light on the subject since it would be odd that a worker who has done thousands changed up for just one car. Just exploring through discussion