I sold my R33 last friday.. for about $1000 less than I was hoping (when you take into account i sold it to somebody interstate unregistered, etc)..but otherwise was happy.
formally on the market for about 3 weeks.. mainly internet forums but not too much interest. Then just when I was getting serious with trading post, carsales, etc it sold very quickly. That could have been co-incidence though.
I'd definitely recommend carsales.. $10 until it sells, and gets good traffic. Trading post, just do "pay on sale". Your ad might not grab attention immediately, but if somebody is genuinely after a skyline, they'll scour it until they do see it - but there are many types of buyers.
Internet forum advertising is largely waste of time IMHO - but just put up the pics, specs and history and that will cut 99% of the time wasters. But you never know, I bought the R33 through here, and my r31 thru another forum forsale section. So cars do get sold that way occasionally.
good luck!