voltage reduction via a resistor will be based on load.
your coil and your lamp assy are NOT the same load.
if you have a front mount and the oe coil.. you need the oe resistor and a proper converting resistor to drop primary current to a max of 4a.
if you are sidemount and oe coil.. then just the resistor.
me? i'd squander the 35$ and get 3 new lamps and a new coil if sidemount.. if front mount.. tat will be about 45$.
otherwise, if you can do without a tail lamp, you can open upt he 2 front lamp shells and wire the front lamps in series and run them that way.. when one pops you lose both as it breaks the circuit.
you've spent 'this much' so far. go ahead and finish it off and not have to worry about it.
the resistor and coil, vs new coil isn't the issue. the lamps are the issue.. you won't be happy trying to come up with a fixed resistance to run them correctly..