I found the same thing a month ago on my 56; thought that maybe the bolts had broken. Then I remembered reading on this website that Chevy liked to hide the occasional bolt/nut, so I removed the pan covering the flywheel, and there they were!
A lot of good nuggets of information in the postings here, read them when you get the chance, even if it is not something you are working on. You never know what you will learn.
