I’m pretty sure that is the one!! Dioch yn fawr!!
Also, I got books from the library years ago, like Y Mabinogian, Y Gododdin and Dafydd ap G, but I’m not sure if one still can!! This was in Yorkshire and Harrow, I think!!
p.s. Found this
Tim Savage collegestreetbooks@btconnect.com
hope it is helpful. It isn’t browsable, of course, but he may give help if you ask for types of book!!!