The majority of Fenton 45's were pressed at American Record Pressing in Owosso, MIchigan. There were one or two exceptions among the first releases but almost all of the rest were done at ARP. They did not use "multiple plants" hardly at all.
The block print design on the Ken Rank record was used on a few others around that time (Ray Hummell "Fine Day", for instance) and seem to fall in between the end of the music note design and the start of the six diamond style. There are other releases that use the generic block print randomly scattered throughout the discography but there are a few clustered together that fall between the end of one and the start of another.