Jaye i fail to see where he mentions S13 seats? I can only see S13 4-stud rims, which you have!!
But yes, as Jaye says, R33 GTS-T seats fit in, of course R33 Skyline being Nissan. With enough effort you could made many things fit... But im not really sure, im going down a new seat path soon too.. Havent decided which yet!
Also, WELCOME!!!