'72 Austin Mini Dsitributor problem
 

Hello all, I've got a '72 Mini that has a broken Distributor cap. I ordered a replacement from Mini mania, but it doesn't fit. The prior owner changed the distributor and I have no way of knowing what size distributor cap is required. Can anyone give me some insight? Here are some pictures of the distributor.

imgur: the simple image sharer

imgur: the simple image sharer