Yes, the 322 (3 cylinder Yanmar gas), 330 (3 cylinder Yanmar diesel) and the 332 (3 cylinder Yanmar diesel). The 316 Onan is similar, but with only one brake pedal.
Because diesels cost more, and in the 1980s it was harder to find than today.These sound like an improvement. So, why does the 318 seem to be the "Holy Grail" of GTs?