Comparison of 1957 and 1958
Chrysler Tail Light Housings

Both tail light housings below are from the passenger side.
The 58 is on the left, the 57 on the right.
Notice how the 58 back up lens reflector and brake light reflector are raised compared to 57.
Don Verity adds that the back up lenses are different 57 - 58.

A closer look at the upper sections shows the rounded edges on the 58.

The 57 edges are wider. The center section of the 58 is recessed.

This is 57 New Yorker wearing the 58 tail light housing.
The fit of the 58 housing is as good as the 57, if not better.
I don't have a 58 Chrysler to make the comparison complete but
it is my guess the 57 housing will fit a 58.

Why did Chrysler shrink the tail light lens in 58?
Styling? Maybe.
Or, possibly the large lens of 57 did not illuminate
brightly from one bulb and shrinking the size of the lens
made for a brighter tail light.