With that SN it would appear to be an early 56 unit.
As for converting 6v to 12v to eliminate a resistor??? Be a tad more specific. generally, the 6v units dind't need a resistor inline with the coil, like the early fords did, but instead just used a 6v coil. Now if you went to 12v and kept the 6v coil, then you needed to add a dropping resistor, or simply use a real 12v coil.
The only other place i can think of a resistor being is in a lamp dimmer switch or a 'tickler' switch incorporated into the lamp switch, or main rotary knob to control generator output. The tickler portion of a switch made to further excite the genny field will probably be rendered useless depending on how you achieve 12v. most just hang an alternator .. 3 wire job, or 1 wire job.. etc.
Be a tad more specific about what you want to do. I have worked on plenty of these old tractors, including IH.. they have pretty interesting ignition systems, in some cases, with ignition power drawn off a tap on the VR.. etc. If I can be of assistance.. just hollar!
Soundguy