I had no problems with unleaded in the Sprint ('87 model) and haven't retarted the ignition.
I sometimes use Shell's V-Power Racing, pressumably 99+ octane, and noticed a slight improvement in performance. In Greece at least, even the leaded "Super" petrol was seldom more than 95 octane actually, but all that changed during the last 5-8 years.
If you do less than 15-20K km per year, I don't think you'll have any problems with unleaded (to engine longevity, that is). If you feel uneasy use a lead additive from time to time. It would also be a good idea to use a high grade fuel (98RON Unleaded and such) every few fill ups.