Sorry, I was in a hurry when I wrote that. Let me be a little more clear.
When I checked with a ohmmeter, there was no connection between the source of the jfet and Gnd. Not good. I've checked, and double checked, and soldered this joint twice and there still was no connection to ground. So I popped the inductor back in there, and ran a green wire from the source pin to ground and... it worked! 52 volts.
For completeness, I disconnected the green wire from ground (not from the jfet) just to make sure soldering the green wire didn't fix the bad connection somehow and, sure enough, the output voltage went back down to 8.8 volts.
So I suspect a bad board.
Normally I'm all about the green wire fix but in this particular kit, with this particular fix, I'm not so sure about the safety. I mean, it looks fine to me, it's just ground, but I'm no expert. Please advise.