It shouldn't matter much that the book is written for pipes in G, just play transposed to begin with (i.e. do what Butler says with your fingers and let the pitch take care of itself).

You will eventually want to play untransposed, because folk tunebooks are written at sounding pitch and you won't want to manually transpose every tune on paper before playing with other people. Recorder players all do that mental trick, it should only take a few days to get the hang of it.