The easiest and quickest way to get to 100% good is to give the gold to a beggar instead of donating it to the Temple of Light.
I noticed that for each donation to the Temple of Light there's a maximum of 75 good morality points. This means a lot of donations to get to 100% good. However, there is no such limit when giving the gold to a beggar which means that the more you give gold wise, the more good morality points you'll get. So in one (hefty) donation to a beggar you can get from 100% evil to 100% good at once.
If you're looking for a beggar you can find one sitting near the end of Bowerstone bridge.