If my memory serves me right Hudson introduced this in 57.I had a hornet whitch was ugly as homemade sin but fast as hell. AMC bought out hudson.Hudson used packard v8s till 57.I do rember it had the GM dist. with the window.Front seats folded down to meet back seat makeing it a big bed on wheels.Wish I still had it.
Nash-Kelvinator and Hudson merged (with Nash holding controlling interest) in 1954 creating American Motors. The AMC 327 did debut in 1957, but was a derivative of AMC's first V8, the 250 ci. version that was introduced mid-year in 1956. And as you said, AMC used Packard V8's for model year 1955 and early 1956.
The Rambler 327 was a very tough engine. Here is a nice 327 Rambler that I made some custom racing parts for.
There was a dealer in Mesa Arizonia Called Randall Rambler. Do a search on them. They has some quick stuff right into the 70's. They even made a 401 Gremlin that you could buy in I think in 1972