Are you dealing with the wiring still intact other than the lighting wires? (obvious, but FYI the volt/amp numbers posted above are reversed hehe)

If you are, simply fire the tank up and check the voltage to the stock light wire once the tank is "running", after the startup flashing portion. If I was to that point I'd do it for you (since I need to know as well) but my wiring is all broken/hacked up for my build so I can't just plug it in.

Resistor can be anywhere along the wire.

You can solder as close as you want, as long as you don't heat the LED up enough to melt the plastic. The more time you have to heat the leg to get the solder to flow, the more likely melting plastic will be. Can you make the legs thinner (sand, grind, whatever) to fit your application instead of cutting them short? Kind of like the stock HL light(s), that use the LED legs to route through the body.