The theoretical rotational accuracy of the system using the flex plate (164 tooth) and a 10 tooth pinion and 10 microstep is 0.011° this equates to a cord length of 0.003'' at the circumference of a 28'' dia circle.
I maintain that it is possible to achieve zero backlash in the gear train using a stock pinion, possibly requiring some OD reduction of the pinion. If I am wrong here, I will build a zero backlash pinion that will work, at no charge.