1. 351C 71-3
L25 K613J

2. 351C- 71-3
G24 KK616JG

I suspect #1 came from a 71 Must Mach, while #2 was from a 71 Torino.

Do these tags tell us anything?

Unfortunately, I don't believe anyone has the breakdown on change levels or plant codes. I can tell you the plant codes denote things such as 2v or 4v, automatic or manual trans, which cam, which heads, A/C or not, which alternator, and other spec like that.

Another thing that helps a bit sometimes is that on the bellhousing area behind the driver's side cylinder head there is usually a partial VIN that tells you year, plant the car was assembled at, and the unit consecutive number. For example, a 1F123456 would tell you the car was a 1971 {1}, assembled at the Dearborn assembly plant {F} and the car's last six digits of the VIN were 123456, the 23,456 car built there that year. That would help you because in 1971 only Dearborn built Mustangs and Torinos were only built in Atlanta. The code for Atlanta was A.