Here is a good webpage with basic sauces by region.
http://vespawoolf.hubpages.com/hub/ribsrecipe
My advice would be to start with the Kansas city one, then side by side taste test it to figure out what you need to add or subtract.
When I am trying to replicate something, I like to pull out about a fourth of a cup of the undoctored sauce and add a little bit of the flavorings to make sure I am on the right track. I've often over seasoned a sauce then ruined it by adding too many ingredients to correct for two much sweetness or heat.
I'm a big fan of apple cider vinegar in sauces, make sure it is real apple cider vinegar, the cheap brands are vinegar with apple cider added in (found out the hard way, it was way too strong in vinegar taste). I don't think you can get better apple cider vinegar than Bragg apple cider vinegar. Sometimes it's in the organic or health food section of regular stores and not with the regular vinegar.
For adding heat without changing the flavor add cayenne (ground red pepper) for adding smokiness and heat add chipotle powder (I like Penzeys) there is also a smoked parprika that is very nice but I am not a fan of too much paprika flavor.
The idea to modify SBR is a good one, just make sure to simmer the sauce with the new ingredients to really develop the flavors.
Personally I like brown sugar more for sweetness than molasses, it's just easier to work with and the molasses can overtake a sauce very quickly.
Good luck and post us your final recipe!