Sounds like one for me, this..!
Harry was never convinced about dowsing, and in his mind the lines were purely sightlines of aligned sites - hence his name 'the Glasgow Network of Aligned Sites'. They are not just highpoints though - there are other mark points along the lines as well, and there are also many sites that many dowsers consider 'sacred' or power spots.
In answer to your question, you can certainly dowse Harry's lines, and I have done so many times on various alignments of his. Some of them are more energetic than others and will dowse as wide as 5 or 6m across; others are less energetic and quite narrow.
This is also a perfect opportunity for me to plug my dowsing workshop at
Ladywell Crystals & Healing in the High Street on Saturday 10 March, at which we will be dowsing a couple of Harry's leys from the Necropolis. Come along and try it for yourself!
Grahame