Thanks again.
The plan is to travel to Tralee on the train (remarkably, it's only just over £100 each for a return, including the ferry from Holyhead, from our starting point in Chester). It's a 10/11-hour journey to Tralee, arriving on Saturday evening, and we'd need to catch the return train from Tralee early the following Saturday morning, giving us six days (Sunday to Friday) walking time.
I had already checked out the buses - if we start from Dingle we'll get off the train in Tralee at 6.51pm and catch the last bus (8.10pm) to Dingle which gets there at about half nine. If, on the other hand, we stay over in Tralee and walk to Cloghane we're relying on catching the (weekly) Friday bus that you've identified, which leaves mid-afternoon from memory - so that does mean we'd have a deadline to keep on our last day walking, which is a point against that plan.
The guidebook has just arrived in the post so I'll have a good look at that before we take the final decision, but Dingle to Tralee is looking more and more likely.
Thanks for your interest! I'll post a trip report if it comes off.
Dave