The 4.30 axle only came on the late B20 Amazons. I don't think they were officially sold in the USA (?). The 4.30 isn't shown in the B18 parts but is in the B20 one. Unfortunately the B20 book doesn't give any of the extra details that the B18 one has on the bottom of most pages. 123GT has 4.56 + OD.
1800 models paralleled the Amazons as far as axle ratios went. Just a handful of early, no OD cars. Late ones and ES had 4.30 but I have read of a ratio under 4 used on the ES. 3.93 maybe?
Specs certainly varied for each market. Here in the UK we always wondered why all the Amazons in the USA came with twin carbs when there was a blanket 55 mph limit at the time. Here, only the 122S had twin carbs and the auto was an option on the 121 only which had a single carb. I have a '65 121 with a downdraught Zenith 36VN. I've got 175s on the back to help with the gearing as Ron has mentioned. It's 4.10 + 4 speed. There's an OD box in the garage though...........
Your car looks very nice Ron. I wondered what you drove after reading your comment about Hondas!