VIN stamps

Hi to all! While I have visited this site on numerous occasions, I have finally joined. My hesitaion was the fact that I do not own a K Mustang. However, I have had a 66 Mustang in my possession since 1973, and continue to own two 66's today. One is a FB C code which is built for open track use with a 302 Mexican block based 347, AFR 185 heads and vintage tripower. The other is a factory GT convertible, A code, 4-speed Pony car with many options and dealer accessories. It is currently undergoing a full restoration. I have always been a huge fan of the 289 Hipo, but have never been able to find one I could afford. Twenty-five years ago, I ran into a guy who had a 289 Hipo short block for sale. He had used it for drag racing many years prior. He told me it was a service replacement block. It did have the proper casting numbers , correct rods and the typical orange paint daubs on the crank. The pistons were the Ford C90X over the counter pop-ups used on the 351 W head conversion. This engine sat in the corner of my garage until about two years ago when I decided to use it for my convertible project. I had acquired all of the unique hipo parts to complete it, and had the engine rebuilt by the same shop that did my 347. Once the block was tanked and cleaned, I found a VIN number on the rear lifter valley shelf. I had never seen one here before, and it is difficult to make out properly since some of the characters are overlapped. But you can certainly make out 5F07K. So much for being a service replacement. Anyway, was wondering if any of you have seen a VIN stamped in this area?