The Encyclopedia of Shinto
I use it to check stuff like what kind of staff we could find at
hypothetical department of rites
, but it has a lot of information that can be cribed for Rokugani state religion, Shinseism/Fortunism relations, etc...
The O-Umajirushi, a XVIIth century heraldry scroll . This is a translation which the author made available as pay what you want, but you can also buy as a physical book. It is also avilable in full on Google Books . An amazing list of Sashimono, Nobori, Ko-Umajirushi and, of course, O-Umajirushi.
Edit: Didn't notice I had been ninjaed on the Encyclopedia. Sneaky Scorpions.
Edited by Suzume Chikahisa