The three different sizes is a carry-over from the Syracuse guns. They were offered in three frame styles, Medium, Heavy and Extra heavy frames at no extra charge. The difference is in the size of the breech balls, the larger the frame the longer the pins.
The ones on eBay do not give a size. They were only made one size regardless of frame. Syracuse guns were not made in 8 ga.
Here is a drawing of the bushings.
A #7 drill is .201 for he counterbore, and a #24 drill is .152 for the striker opening.
You didn't list your "A" dimension. Let me know. I will make you the mediums, if they don't work then I will make the large ones.
