I have two fonts of this acrylic type. I was told (I'm not sure if this is true) that they were a copy of a wood type font that was made so that they could get a clean & sharp print to then copy for photosetting from back in the 60's. (for offset printing) A lot of the wood type around would have had dinks / scratches which they didn't want to replicate.
Personally I think these are from the 80's. They are acylic mounted on multiply wood & you can see the router marks.
See a description of Photosetting here : - http://en.wikipedia.org/wiki/Phototypesetting
It's easy to forget all the different transitional phases in printing history.