Soft Plastic question on 554

[HowardPgh]

I am currently restoring a black 554 wall set from parts. I found one with a black metal hookswitch base, ringer, network, and metal fingerwheel dial all dated 1957. I have a bakelite G1 for it.
My problem is finding a black case for it. I have several of those, oldest being 1960 which is totally trash. I have a 1964 dated case, would that be the soft plastic. (how long was the soft plastic used for the 554s) I also have several later ones which are the hard plastic.

[TelePlay]

If you put a small drop of 70% Isopropyl Alcohol on a clean area inside the case and let it dry by itself over several minutes, if it leaves a ring in the plastic that can be felt when running a finger tip over the spot, it's soft plastic.

If it does not, it's ABS, hard plastic.