KZ650 exhaust identification

I have two sets of 650 exhaust, one is off a C2 that I bought this Summer and one I bought off the internet recently. Both have the same part # but the set I bought off the internet also has S-1978-12 above the #. The S-1978-12 set also has longer heat shields (the heat shields are interchangeable) and it also has 6mm drain bolts on the bottoms of the head pipes. I have looked at the parts diagram on the Kawasaki web site and it shows the 6mm plugs on all the B and C models. I restored a C1 a few years back and I'm pretty sure it did not have the plus and had shorter heat shields. Any ideas? Thanks.

Those plugs in the header pipes were not used on the 1977 KZ650 models. They first appeared on the 1978 models. Also, the lettering on the mufflers of the 1977 models did not have a date on them. The letting on my 1977 KZ650-C1 is shown below. The long muffler cover (heat shield) is from a different KZ650 model, not a B, C, or F model. Ed

The muffler covers may be from an 650D SR. The SRs had criss-crossed header pipes.

Ok, so I think that the pipes that came on my C2 are probably left over from 77 because it is a very early 78 ( produced 10/77, frame number 013693). So would the set with the plugs came on the later produced C2's? Thanks.