Mark,
In a 1974 printing of the parts book, I see some components of the distributor listed for the 1493 and it shows 69-70. Looks like the 1493 may have indeed been used for at least part of the 1970 model and then changed to the 2021 later. My guess is that your 2021 is the correct unit for your car. Bet Joe Lucia would have more definite info as I'm sure he has a 1970 printing of the parts book.
In a 1974 printing of the parts book, I see some components of the distributor listed for the 1493 and it shows 69-70. Looks like the 1493 may have indeed been used for at least part of the 1970 model and then changed to the 2021 later. My guess is that your 2021 is the correct unit for your car. Bet Joe Lucia would have more definite info as I'm sure he has a 1970 printing of the parts book.