This merger was not between equal partners, being essentially a takeover of Hudson by the Nash organization. The Hudson design dating back to the 1948 model year was abandoned, and 1955 Hudsons were based on the Nash body design introduced for 1952; this link discusses that model year's Hudsons.
Creation of a Nash-based Hudson design was a crash project. Most American car companies announced their 1955 models in the autumn of 1954, but there wasn't time to style and implement what amounted to a Nash facelift in that time frame. I suspect the team working on the task did well by getting '55 Hudsons launched early in 1955.
Hudsons were given a noticeable facelift just before the merger with Nash; I discussed the design here. The grille design was a departure from a theme used since 1950, but was not carried over for 1955 even though it might have been.
This shows a pre-merger Nash. Its basic design served as the basis for facelifted 1955 Nashes as well as for 1955 Hudsons.
General Motors introduced panoramic or "wraparound" windshields on all Oldsmobiles, Buicks and Cadillacs for 1954. Most other car makers, including American Motors, responded with their own versions for 1955. The basic Nash body was retained, but besides the new windshield the facelift included a new grille/headlamp ensemble, reshaped front fenders and revised character lines on the sides. The front wheel cutout was slightly enlarged, but this did nothing to relieve the slab-sided appearance.
Here is a partial view of the grille design along with material related to features inherited from Nash. According to this book, that design was similar to what Hudson stylists had been considering for a facelift prior to the creation of American Motors.
The Wasp was Hudson's lower-priced model, but its styling was essentially that same as that of the top-of-the-line Hornet. The main difference was Hornet's cowling to front axle line distance was slightly greater.
Hudson retained the headlight placement of '54 Nashes. Besides the grille and front fenders, the main differences from '55 Nashes were in the side character line and chrome trim and, especially, the large wheel cut-outs that largely eliminated the Nash's heavy, slab-sided look.
A view featuring the rear. The rounded forward edges of the backlight represent another slight change from Nash.
Hudsons for 1955 were stuck with Nash's bulky basic body. But the hurried facelift resulted in a fairly pleasing result given the circumstances. Unfortunately, Hudsons now were pretty obviously Nashes despite their disguise, and this probably did not help sales, which were around 20,000 units. Worse were the facelifts given Hudson for the 1956 and 1957 model years, the latter I discussed here.
And why did I used the word "Hash" in the title of this post? It's because that's a term some people applied to Nash-based Hudsons in those days; think Hudson+Nash = Hash. The word "hash" has more than one meaning, at least for American speakers. One has to do with a type of food that is a combination of bits of meat and bits of other ingredients -- something that might imply the Nash-Hudson mix. Another meaning has to do with making a mix of things that yield an unfortunate result, as in the phrase "they made a hash of it." That also might apply to American Motors' attempt to keep the Hudson brand alive.