Got the replacement "hybrid" axle from Lippert (shipped UPS, which had the delivery guy shaking his head at the size and the weight label that claimed it weighed 47 lbs). Took about 3 hours to R&R, doing a bunch of measuring and thinking before doing - the actual process was pretty quick. No modifications to anything - unbolt old, bolt in new.
With the hybrid axle and the 15" wheels, the trailer sits a good 2"+ higher than before, which is a Good Thing, although it will mean completely resetting the hitches and antisway.
The two axles
NV: 231694 (old)
NV: 257699 (hybrid) 5200# beam with 3500 # stubs.
These are both supposed to be 22deg unloaded start angles - look at these pics (yes, taken from slightly different angles and rotated). The old part (and this is NOT the bent end) is clearly different. Check the space between the stub and the mounting hole.
Thanks to Lippert who sent the hybrid and attachment kit directly to us, with relatively little fuss. No thanks to Forest River, who ran us in circles for a bit.