I have done this before although it was ages ago and I sold the bike to a Toronto messenger when I left the biz. it worked just fine for me for the 3 or so years I had the bike-great winter bike as the brake in the coaster is not affected by adverse weather conditions-run a front brake too please!! as for finding a decent hub-you just have to keep looking...If I remember the stock cog on my hub was a 17 or 18 which i ran with a 52 ring-hey my knees were young and strong and the bike was just mainly for delivering not for touring. good luck!!
Matthew, Calgary AB