Hello & welcome
Either leg length will fit a Gibson LP - long leg is the original Gibson spec, but unless it sits VERY proud of the mounting ring, short leg will fit too (even then, you can always cut the spring down).
4 conductor wiring gives you the option to coil split (NB: you don't have to wire it in). Might as well get this even if you don't plan to use the coil splitting right now.
For spacing, measure the distance between top-bottom strings over the pickup pole pieces. Choose whichever option is closest to that distance.
Hope this helps