publication rights for anothers work?

hi there guys, don't believe the name by the way.
i recently bought an antique sketch book of coats of arms, not such a big deal i hear you say. well normally i would agree but the sketchbook appears to be some of the preliminary work of alfred w morant who is best known for his works on heraldry for the papworths ordinary, it contains many hand drawn sketches and notes which have not been published anywhere, it contains the churchill and spencer heraldry as well as many others. morant died in 1881 by the way- so where and how would i start to get some sort of rights over these images. btw a similar sketchbook by morant is held in the national archive , would this have any bearing on it. thanks for reading and merry christmas.