The subject says it all, really. I got ahold of a couple of 74LS259D SMD chips, soldered them into the adapter board, and replaced the ‘259 stack in the HRD+ with the daughterboard.
Since nothing ever works correctly the first time, I botched a solder joint on one of the chips and spent an hour with a microscope, a schematic, and a continuity tester to track down the problem.
Anyway, it works. Eagle .sch and .brd are here. Enjoy.