Hi smauggie
According to my Minkus catalog:
1917-20
Gold currency, engraved
imprint at foot except on 3c
1. Rouletted 14½, thick paper
2. Perf 12
thick paper (1c-5c)
medium to thin paper (5c - 5p)
Note after the llistings state that these stamps were not regularly issued.
For more info post your question to MEPSI:
http://www.mepsi.org/ I've done that before and got a fairly quick response. I seem to remember I had to submit my question to the membership request because I could not find any other e-mail addresses on the site.
Jerry B