I think it's worth trying to feed the angelfish separately to see if that reduces any aggression issues. It's possible that if it's well-fed, it'll be less inclined to chase the neons or corydoras. I do recall reading a thread recently where people were discussing the minimum tank size for angels, and there was quite a bit of disagreement about whether 75 gallons was really necessary. Unfortunately, I couldn't find the thread again to refresh my memory.
It might also be a good idea to have a chat with the person who bought you the fish. I'm sure they were trying to be kind, but it's always better to get the fish yourself so you can choose the ones that will work well in your tank. I remember when I asked my partner for a betta for Christmas, I ended up going out and buying one myself just to make sure I got the right one. Maybe you could explain to them that you appreciate the thought, but in future, you'd rather have the money to choose your own fish.
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