I think the Gd was ground - 'gardens' in that part of Douglas both then and now are few and far between (it was also a near slum in parts judging from some photos - I will refrain from my usual comment on present architectural practice in Douglas) - Shaws Brow is now an ugly carpark.
Also remember that there appeared to be a PO renumbering sometime in the 1880's as street numbers for many properties seem to shift by 1 or 2 (eg numbers on North Quay which I could say at times appear to be nearly random choices).