Need some tech help.

Ok, i have that BluArc distributor in my panhead and im going to put new points, etc, in it.
the one in the middle is the one that was in it. the two others are the 2 different replacement ones I have gotten for it. The contact to the cap is obviously different.

my question is, what exactly is the difference going to be, timing wise and how it runs.

i think it determines dwell, but as i have never actually fucked with distributors in the car world, other than just replacing parts.

so, anyone want to explain???

thanx
D

In case you were curious