All the N/A 33s have 4-stud wheels, apart from the rare few who have had a conversion to 5.
Standard wheels were 15 (probably x 6.)
Wheels that fit the Silvia/180sx don't automatically fit the Skyline, and the selection from what I have seen is really poor. Hence, after over a year I still haven't found new wheels. However, the ROH Drift Rs seems to be the pick.