Getting from Dublin to Glasgow

We did something similar.. Flew via Easy Jet. I think you could go by ferry and then bus but flying is easiest. Just watch carefully this airlines restrictions.

Multiple airlines fly between Dublin and Glasgow including Aer Lingus and Ryan Air. Choose which ever airline meets your schedule and your budget.

Flying is the easiest and fastest.

You could do the bus-ferry-bus route but it will take the good part of a day.

After finishing a tour, you will be tired. Why not make it easy on yourself and just take a flight. I've done this route a couple of times.

The good news is, no immigration in Glasgow. From Dublin to Glasgow is like a domestic flight.

If you want try something a bit more adventurous, you could take one of the multiple daily trains from Dublin to Belfast. From there, several ferries a day go from Belfast to Stranraer, Scotland. And then the last leg is a train from Stranraer to Glasgow. This would probably take at least a day, but you'd get to see more of the British isles.

In 1999, a flight I took from Dublin to Edinburgh didn't even cost $100 and took about an hour. I wish I had taken the train-ferry-train option just to see more.

A train every two hours DUB to BFS, not dozens a day [post since amended to multiple trains]
These days the ferries go to Cairnryan.
The bus connections to Stranraer do not work at all. Currently due to the fire at Ayr station all the few trains a day are bus replacements.
Far better to catch the connecting express bus to Glasgow.
Or even better the Hannons bus from Belfast to Glasgow which drives on and off the ferry with you on board.

Ryanair has so many cheap and frequent flights. That's what we did and then trained to Edinburgh. Scotland is amazing. Just remember they use £