how did someone figure .67 ratio reducer? what pinion are you using now? i don't think the math is right.
Small tires and high (numeric) axle ratios generate speedo cable speeds that can't be corrected with the available 16-21 tooth early pinions. The .67 reduction allows the user to alter the normal math to choose the correct pinion.
As I stated earlier, the OP's combo would require a 23-tooth pinion which was never available so the .67 reduction would call for a 15-tooth pinion which, also, was never available; so a 16-tooth would be the closest.
That's why an inline reducer is more practical, they allow for a wide variety of reduction ratios.