Well done on rescuing this ram and giving him a chance. Over the years, I have rescued many ill treated animals from dogs up to big horses.
You have wormed him which is the first step. No amount of feeding will do any good if they are carrying a worm burden. As he is under nourished he will be lacking in vitamins and minerals, which is probably why his fleece is coming off. It takes quite a bit of time to get weight on any under weight animal, and at this time of year, with grass not being plentiful, it is hard to get them looking good. But I have found the secret to feeding them, is little and often. Their stomachs are not used to food basically, so they cannot cope with large meals, and its likely to come out of the other end pretty fast. So, I would split the feeds into three or four meals a day if thats possible.