I cannot say, although many 'groups' called sedevacantist are not - as someone among their number claims to be sitting on the Throne of Peter.  This includes the 'Popes' Michael, Pius XIII, etc.

As for others, there is the CMRI, the SSPV, the independent priests throughout the USA (Bps. Sanborn, Dolan, McKenna, and Neville, Frs. Cekada, Collins, Thielen, Stepanich, Saavedra, Selway, McGuire, Ahern, Cyr, etc.).  There is the Instituto Mater Boni Consilii, in Italy (they have a seminary, too).  Some independent priests and bishops in Europe, South America, etc.

As for actual, doctrinal differences, there are none of any consequence - granting that the crazies are left out of account.  I can tell you more later, but I need to read, pray, and sleep.