My 55 also has the toad skin look & feel.
A friend on his 56 had his painter replicate it by dribbling on a very thick heavy primer to create the small bloches.
When that dried he used a flat black to overcoat it.
It looks factory original!

The assumption it was done to reduce glare is probably correct.

1 1955 Chev one ton. 261 engine

3 1962 Chev c-10 261 engine
4 1966 Plymouth VIP 5.7 GenIII Hemi
5 1966 Imperial Crown Coupe 440 engine