12558693 = square coil
19005218 = round coil.

Its really just the difference of 1" in length on the wires.

An easy way to remember it on the fly is the P/N for the square coils have no "round 0's" in it.

 

Hey thanks Signal25 that helps!

 

Hey guys just wanted to give you all a heads up. I got the tune up done and all the fluids changed in my H2. The truck already ran great and now seems to runs even better. I changed the plugs, plug wires, fuel filter and had the front diff, rear diff, transfer case, brake fluid, coolant, oil, and transmission fluid changed. I shouldn't have to worry about any maintenance stuff for a while now. Been getting between 11-13 mpg(hand calculated) on every fill up so curious to see if all this might help a little.