There's a reason I was specific about this in my long previous post: If you didn't buy the car new, you have no way of knowing what was done prior to your ownership.
A defective part will usually reveal itself within the first year or two. In this case, the ink was barely dry on the calendar 1968 year-end paperwork before the tachometer part number was superseded. If the original tach failed in April of '69, the dealer would've replaced it with the only unit available at the time: the upright-numeral sidewinder 1969 part. If it failed a couple of years later, the owner may have DIYed it with a junkyard tach. No one can say for sure.
Am I saying a car couldn't have been built that way? Of course not. But if you didn't buy the car new or own a dated day-two photo of the dash, it can't be considered a solid reference point. By the same token, with currently-available information it's equally difficult to say it's wrong. Isn't restoration fun?!
