Thanks. I placed the .DAT files in the OpenRCT/object folder, but they didn't show up in the scenario editor (with all the addons and custom ticked.) I also tried putting them in OpenRCT2/data/object/rct2/footpath folder, but nothing. Might it be something to do with having to convert them from .DAT to .json?
Edit: working now, seems it didn't like using the launcher...