So you are converting the car to 12V? Then there is absolutely no need for a "67 1500" starter.. Why run it on twice the current it wants instead of just using an ordinary 12V starter that will do the job much better and is so much easier to get..
If you were to run a 6V starter on 12V you could just convert the rest of the car and leave the engine in there and not change either the flywheel or the starter
The only issue I have had doing this is that the starter may "steal" all the current while cranking the engine (at twice the speed) so there is nothing left for the ignition. Resulting in an engine that you can crank forever without getting it started but it will fire as soon as you let go of the key
If you do it "the proper way" you will have to change the flywheel, starter and clearance the trans for the larger flywheel. It is very self explaining where to grind when you see it. An old trick is to put the engine as far in as possible and turn it so the teeth will leave marks but it really isn't necessary. Having a loose flywheel to measure up will do fine.
