I have an idea aout the 3HF tags. How many of the 3HF cars are 4 speed cars. We all know that the 3F is the 400 option. Well, H was the sales code for the 3.36 rear axle ratio, this was the standard rear end on the 400 4-speed cars and an option on other cars. Could it be that this was stamped on the data plate as so?I'd also ask what the PHS shows as the original rear end on the cars that have 3H and are not 400 cars. If they are 3.36 (which was optional on all cars in 67), then this could possibly solve why there are tags mrked 3HF. Just my opinion.