Spilotro belonged to the Melrose Park group and so he was possibly Nicolettis and Aiuppas choice while Accardo probably only gave the ok.

Im not sure if Roselli had his own base or territory in Chicago since it seems that his only connections were Ricca and Giancana. He also had connection to LaPorte just because he was some sort of voice on the west coast for the Outfits bosses. So in 1966 Giancana was out of the country while by 1972 Ricca was dead, which perfectly fits with the same year when Spilotro arrived.

I think that Rosell still had interests in LA at the time and also Vegas, since besides taking care of certain interests in the casinos, he also was involved in the garbage collection in that same town. Also story goes that in 1968 he wanted to take over the LA fam