Hi Stew,
The only time Don Young described with drawings the sight glasses for his hydrostatic displacement lubricators was in his series on 'George', his version in 3.5"g of the original Ffestiniog locos. It is a twin glass design, as you require.
If you PM me with your details I can email you the drawings and construction notes, plus a few hints and tips.
Cheers,
Julian
Edited By julian atkins on 06/11/2016 20:45:30