I found it to fit very well - There were more factors than just the touch hole (as you know) to make the barrel fit - The tang, the fit of the breech against the wood, the already cut inlets for the lock and plate - so my best bet was to align the barrel to the proper position based on where the lock plate actually sat. (Back and down)
Last pre-carve for me... it's a juggling act to fit all these parts together with a roughed out form of what it is "supposed" to look like - my stock must have shifted in the mount while carving, as nothing lines up.
Just set that barrel in tight and align the touch hole like in my drawing and your swamp barrel will remain just fine in the forstock.
Jon