Hmmm looks like the Newport argument may hold some water.
The Newport arguement may hold some water but what I found totally Discounts it.
Through my research I seen that one article stated the Newport's had inherited its Styling Cues from the new yorker and another article stated that The 1975 Chrysler models looked similar in which the three that looked the same were the New Yorker, The Newport and Town and country. in another article about the history about the New Yorker here is what they say
In 1974 the New Yorker (C body) was redesigned dramatically. This design carried on for five model years. The 1974 - 1978 New Yorker used the identical body as the 1974 - 1978 Newport, Newport Custom, 1974 - 1977 Town & Country, and 1974 - 1975 Imperial. The trim level New Yorker Brougham also appeared for the first time this year. The New Yorker's standard engine in 1974 was the 440 cid big block V8.
From 1976 to 1978 all New Yorkers were correctly referred to as New Yorker Broughams, there were no plain New Yorkers. The styling of this car was carried over from the discontinued 1975 Imperial. This change gave the New Yorker Brougham the beautiful waterfall grille and other styling cues that had been designed for the 1974 - 1975 Imperial. This made the New Yorker the flagship of Chrysler Corporation's lineup for the very first time, but not the last. The 440 cid V8 was the standard engine each year except 1978 when the 400 cid V8 was the standard engine. 1978 would be the last year Chrysler would offer a big block V8 in a passenger car. It is noteworthy that 1977 was the last year for New Yorker's station wagon version, the Town & Country, to be built on a big block powered C body platform. In 1978 the Town & Country was moved to the much smaller M body platform
In my Search For the new yorker I Accidentally stumbled across a Picture of Layhey's Car and found it to be a 1977 New Yorker Brougham. But Looking down in the article I stumbled across a picture that Almost looks Like a Dead Ringer for Ricky's which is the 1975 New Yorker Brougham (I Know that Ricky's car didn't have the piece of metal across the back tire but consider how beat up that car and it could have been torn off). apparently All New Yorkers after 1976 were Referred to as New Yorker Broughams there were no plain New Yorkers.
Now looking from the names of the cars shown that there were a few different lines of New Yorkers in that year but I know it is not the Newport because I have a picture of the Lights from Ricky's and the tail lights look closest to the New Yorker St. Regis (Unable to find the lights for the Brougham) So in any way that you look at it It is defiantly still a new yorker. also while looking for a good side shot of the car, I seen some of the Logos (Painted in black making it hard to see) but after some examination they are New Yorker Logos putting This To rest (Seen in S01E04 -Mrs peterson's dog gets fucked on the back of Ricky's Trunk).
Also another way to tell the difference is in the styling of the side windows. With the New Yorker Brougham if you notice with the windows down there is no separation between the front and rear windows while on the Newport it looks like there is a partition between the front and rear windows.
So even though The Newport used the same body as the Yorker, there is no way it can be because of the logos seen on the car and the design of the side windows.