I went to get a key made for my glove box as my trunk key didn't work. Long story short, my trunk has a B key (1967 trunk key) for it instead of a D. I suppose it could have been replaced, but some of the other parts on my car were 67 leftover parts and I wondered if any 68's got any 67 locks? The glove box lock is a D, but that could have been changed easily too. ???
I think the cylinders were interchangeable. Can't swear for a 68, but for earlier chevys I have several I rekeyed to use the same key everywhere, doors, glove box, trunk, and ignition.
What's the build date for your car? I found the same problem for my trunk key on my 68.
05D. Mine was one of the build dates that got 67 steering parts on it, so I wondered if anything else was used on it from 67. The ignition keys fits the doors etc., but the trunk key didn't fit the glove box. I found out why when I went to a locksmith to get a key for it, that the glove box was a D and the trunk a C. I know it didn't leave the factory with three keys. It would seem to be easier to change a glove box door or lock than a trunk one. But that doesn't make it so. Any other examples?