Was this Model T or earlier?
It appears that this is a Model T accessory high tension mag. It was paired with a Splitdorf aluminum timing cover with a drive gear added. Googling it I found this link that talks about it and has a front view drawing of it installed on a T.
https://books.google.com/books?id=Blo-AQAAMAAJ&pg=PA93&lpg=PA93&dq=splitdorf+for d+special+mag&source=bl&ots=m3P_xQD4bV&sig=QmO8YjXgFssQN6yfXu_G0_a3m1k&hl=en&sa= X&ei=TMP5VL-BCMLXoATd7oGAAg&ved=0CDEQ6AEwBA#v=onepage&q=splitdorf%20ford%20speci al%20mag&f=false
Hope that this is helpful.
Thank you for finding that.
It is much appreciated.