Congrats on the Lisa!
What you believe to be a piece of metal rolling around inside the widget drive is actually a piece of glass. It is a piece that calibrates the head to tell it where it is, basically. Since the drive is toast without it, you might open it up and see if you can glue it back in place. I had one that broke off but I have heard that others had just fallen off with age because of the glue they used. For the record, I couldn't get the piece glued in properly. If you are able to glue it in, you might have to low level format the drive to "recalibrate it".
See what damage the glass has in the drive first and take it from there. Normally you wouldn't open a hard drive but it's "toast" anyway so why not try to McGyver it back to life... even if it is probably futile?