The story I've been hearing about the Sil-Eighty:
Drifters, upon damaging their 180s, replaced the front ends with cheaper Silvia faces. Drifters, and drift fans, began doing the conversion to their 180s for appearance only.
Noting this trend, a specific Nissan dealership or chain of dealerships, I haven't heard which is correct, began converting 180s and selling them as Sil-Eighties, right from the showroom. I have heard reports that they also replaced the 180's CA18 engine with the S13's more powerful SR20DET, which would make the Sil-80 convo make sense, as it won't fit under the 180's hood. (This is why a new hood has to be aquired when doing an SR swap in a US-market 240SX.) About 500 were made and sold. The "official" Sil-Eighty is now a highly sought-after collecter's piece.