Thanks for your message.
Unfortunately I have not had any replies from anyone with a C5 with floppy drive.
There are three DIP header links on the board.(green)
2 have no links connected the third has a link, at the side of the large blue capacitor.
There is a strip of links (coloured green in the photo I posted above.
No links are fitted in this block.
It may all be correct but as the back was off the lathe when I bought it I don't know its history.
If anyone does have a C5 with a floppy I would be grateful if they could see how it is connected.