Looks rather strange unless I am just seeing things. Why is it oblong? Looks like there are TWO keepers.
without seeing it up close I would hazard a guess that is an adapter?(general to ford) if you are talking about base of distributor.
It looks like one of the Ford HEI conversions from Skip White Performance with some added on adapter.
This shop has done some distributor modifications and is well known on the H.A.M.B. http://www.bubbasignition.com/
I was more interested in the heads. Looks like Argentine heads. I think that block on the top is the coil.