711M block casting numbers

[xlcapri]

I have got a few 1600 711M engines in my Capri parts hoard and have noticed that the cast block numbers "711M6015BA" is different sizes. Some of the lettering/ numbers is about 10 - 12 mm in height and shorter in length and some are about 20 mm tall and longer. Im thinking I could be some early blocks and some later, hoping someone can tell me for sure. Also might be interested in selling some 711M blocks/heads in near future.