I know there are a few lovers of grammar here, and I have the occasional grammatical urges myself (I lie down in a darkened room until they pass…).
Anyway, while seeing if I could find any information about the historical development of gender in Welsh, I came upon the following, which is a historical and comparative Welsh Grammar from 1913. Because of its age, it is in the public domain.
http://en.wikisource.org/wiki/A_Welsh_Grammar,_Historical_and_Comparative
I hope it may be of interest to someone.
His introduction is quite interesting, with some digs at earlier " false etymological theories", etc. 