Google turned up this:
Int'l Bittering Units: 15.0
Alcohol by Volume: 5.1%
Malts: 2-Row Pale, Honey, Munich, Caramalt
Hops: Northern Brewer, Saaz, Mt. Hood
I haven't tried it, so just a first guess to get you started:
I'd go with something like 80% pale, 10% Munich, 7% Caramalt, 3% Honey malt enough to get you ~1.050. Bitter with the Northern Brewer (or whatever) and add some small additions of Saaz/Hood in the last 15 minutes of the boil.
Ferment with Wyeast 1007 (apparently the strain they use in 90 Shilling, so a good guess for this one as well).
Check out The Mad Fermentationist
for my adventures in fermentation (cheese, bread, ginger beer plant, and of course plenty of funky beer).