Yeah. The 7100 technically had 40 more watts, but even that thing was too old to provide enough juice. You're really going to want to convert it to ATX. It's so easy even I could do it. And if you get some wire nuts, it's even a solderless mod. If you decide to use a soldering iron, you could add an ON/OFF switch like I did. Then it makes it like an LC. I couldn't get the soft power to work, though.
You just get an ATX PSU that's roughly the same size, take out the innards, then match up the wires using a simple diagram. I got mine for free out of an old Dell computer heading to the recycling.
I only now just realized that it looks like there could be enough room for 2 HDDs in the IIci HDD bracket. With an ATX mod, you could split the +5v and power 2 HDDs, then RAID them.
I'm going to revisit my IIci soon. I seem to recall when I was first fiddling around with it, I had it running on 7.5.5 with MacTCP. I'll give it another go. I do believe that the Rocket Disk itself has to be 7.1. So leave it as is when it creates your first rocket disk.