RobertBryant interesting analysis. The primary cross sections to look for would be for the slow neutrons from the (hypothetical) deuterium photodissociation, whose maximum energy Steinmetz et al. give at 0.087 MeV. Slow neutron capture, as you know, has a large cross section. It's from these neutrons that I'd expect to see most of the activation. Activation of Er and Hf is reasonable to conclude, given that Gd and Cd, the witness materials that were used in the experiment, were also activated, and given that they picked up neutrons in the CR-39 and bubble detectors.
There appear to have been a range of neutron energies present. In the CR-39, triple pits were observed, implying some neutrons with energy >10 MeV.
Although (n,2n) reactions with something in the setup might be possible (I'm not sure how likely), other possibilities include prompt and beta-delayed neutron emission from unstable daughters following slow neutron capture. The following reactions are energetically possible, although I don't have the neutron capture cross sections and branching ratios (and hence likelihoods).
n + 167Er → 81As + 87Br + 91206 keV →β-, →β-n
n + 170Er → 84Se + 87Se + 90336 keV →β-, →β-n
n + 168Er → 84As + 85Br + 89510 keV →β-, →β-n
n + 168Er → 83Ge + 86Kr + 89323 keV →β-, →β-n
n + 166Er → 80As + 87Br + 89252 keV →β-, →β-n
In each of these cases, there is a beta-delayed neutron emission in one of the unstable daughters (e.g., 87Br). My little helper program produced 340,369 of reactions like these that lead to beta-delayed neutron emission. These ones have energies in the range of ~90 MeV, which seems implausible and hence unlikely, but among 340k reactions, perhaps a few are likely. I also see that prompt neutron emission from an unstable daughter is energetically possible:
n + 166Er → 25O + 142Nd + 1746 keV →n
n + 170Er → 25O + 146Nd + 1538 keV →n
n + 168Er → 25O + 144Nd + 1479 keV →n, →α
n + 167Er → 25O + 143Nd + 1433 keV →n
Again, no cross sections or branching ratios to weed out the unlikely reactions, unfortunately, but you get the idea.
Given the vast permutations of energetically possible reactions of these kinds and others, and my lack of familiarity with gamma spectra, I would hesitate to speculate about individual lines in the spectra.