Andrew, you can add a dizzy gear drive on a 59A cam for a conversion to the later distributor. But, to go the other way, you would need to replace the cam to remove the drive gear and get the slot for driving the earlier distributor. And, of course, after you swap out the cam, you would use the early timing gear cover.
You're not going to next ask about putting a flathead into a '67 Chevy II, are you?
