Since you guys seem to be dipping into the Nissan world maybe this can be of some use.
The T28, is a journal bearing turbo used on the S14 SR20DET and the pulsar GTI-R engines
The GT28R, is a ball bearing turbo used on the S15 SR20DET, it has a unique part# and is pretty rare to find, especially on craigs. The pop up in the 240 realm every now and again in the 240 forums, but fetch a pretty penny.
The GT28RS (Disco Potato), was a hybrid ball bearing turbo derived from the GT28R, made famous by the B15 Sentra that was used for the R&D.
The GT2871R is a step up from the RS offering more top end while adding a touch of lag. Most say that the .64 A/R is almost identical to the RS while the .86 A/R is noticeably laggier.
Hope this helps to alieve some confusion and protect you guys when shopping on craigs. FWIW, I owned a 240 for 6yrs and had already performed a S13 blacktop swap before there were how-to threads or it was the cool thing to do. I eventually sold it because the entire community went to hell and it just wasn't where I wanted to be.