For a 66 it's fairly common, especially late production cars. My guess is Mopar built out the early a 6 cyl cars with the 6 cyl part until they ran out and then standardized on the V8 part from there. Later cars were standardized. The early A body was designed to be a 6 cyl car, and the small block was modded in 64 to fit them (LA engine). The different center link was a holdover from the V8 conversion.
For 67, the A body was reconfigured to accommodate both small block and big block V8s and pretty much everything was the same except the mounts on the K-member.