what size/kind of oil pump is right for me?

[petevw]

i have the dry sump pump.
the dry sump pump bolts and is squished onto the stock oil pump. its the stock oil pump i want to replace. the part that sinks into the case. the drysump pump itself is ok.
i see 26, 29, 30mm pumps on the net. i know nothing about these pumps. this is what i'm inquiring about. or i can replace it with a stocker. i don't know.

pete