#1
I have an Ibanez S320 and I'm putting a bareknuckle aftermath bridge pick up in it!
I just don't know what all this means?

Bridge Spacing
50mm / 53mm

Conductor
4 / 2 braided

Leg
Long (1/2") / Short (1/4")

Is there a page that will give me all this information on it!?
#2
Bridge spacing would relate to the string spacing at the bridge, you will want the wider option for you guitar, assuming you still have the original trem (or any trem) in there.

If you want to wire up your pickup(s) for coil tapping, etc, then you will need the 4 conductor, otherwise 2 will do.

The legs are the metal tabs through which the screws supporting the pickup go. I'd go with the shorted, 1/4", version.

Hope this helps.