Interesting--were his ribs purchased enhanced or did he inject/marinate them? Many people (I'm one) feel that enhanced ribs tend toward hammy. What did your dad do for seasoning and how were the ribs cooked?
You certainly could build a rub from a garlic and onion base. If you can use granulated garlic and onion rather than garlic salt or onion salt it is easier to control the final salt level.
For a 'traditional' flavor/appearance use a chile in the mix--paprika. ground Ancho--and/or use a purchased 'chili powder'. Paprika or Ancho/chili powder act as good carriers bulking up the mix and carrying the other spices/herbs evenly during application but using none of any of these is perfectly fine too.)
Thyme works well with onion and garlic as does ground celery seed, marjoram, cumin, powdered lemon peel, sage, and many of the 'sweet' spices like allspice, ginger and cinnamon. Oregano is a component of many 'adobo' mixes and is usually in commercially prepared chili powders. (Sage, lemon and the sweet spices can be overpowering if used in large quantities but are great in small amounts.) You can keep it very simple though, as you wish.
Sugar in the mix will help bark formation but using it is not carved in stone--you can skip it or use just a little and you surely can use white instead of brown. You could make a mix without sugar and then separate some of the mix out and add a little white sugar to that applying the sugared mix to half a slab or so to see what you think.
