I'm not trying to take sides or anything, but I got curious about stampings (font sizes, etc.) and looked through my records to check what was done. It seems as if different font sizes for some letters/numbers were quite common (almost the norm) up to the 2nd half of 1970.
 
Amazingly, one of the photos I found was the next number along from GTV6's car. It's from a car I was looking at buying (and should have bought) back in 2006. You can see from each photo that the font size inconsistency is the same between the two.
 
 
 

 

Thanks Jamie, I think it was sorted by 9/70 as one of my wrecks shows. Maybe earlier. Definitely the 4 was different and a few other numbers (need to check). Number 1 was definitely larger. I do notice that stamp changed from 71 to 72. Position and font. Font different to 71 and 72 model as well.