I'm not sure the Inchicore Sulzers were ever fitted for multiple working. It's likely the photo above was staged, but even if it wasn't there was probably a driver in each cab.
The ban on running nose-first had more to do with the fact that engine noise made it difficult for drivers to hear detonators if they were triggered by the wheels at the nose end.
I wouldn't be so sure about this. They started working in multiple at the same time CIÉ began pairing the other small GMs, too, which suggests it had more to do with power requirements (the hammering they took working alone on six-coach Mk3 push-pulls showed why this was essential). Most termini still had operational turntables up until recently - and some still do - which would have allowed them to be turned, and there are photos out there of that happening. There are also photos out there of single 121s working services into the late 1980s/early '90s, such as the Cork mail. I even saw one hauling a dead 071 once in the mid-'90s.