I've tried looking for direct, factual information online, but it mostly seems to be articles comparing the IRA and Fatah/Hamas. I'm just wondering to what extent the IRA and the PLO (or any other Palestinian groups) worked together.
Yes, the IRA did train Palestinian terrorist groups. Their cooperation was significantly more focused on the PLO and Fatah, than on Hamas. The PLO assisted with training IRA operatives in the 1970s, thanks to the support of Gaddafi for these groups. This continued with cooperation, though the extent varied over time with political events, such as attempts to place some distance between the PLO and the IRA after Lord Louis Mountbatten's murder in 1979, as some accuse the PLO of assisting with the financing of the operation.