It looks like you all have done some great initial investigation about the options in front of you. I wanted to chime in with just a couple of suggestions:
First, several of you have mentioned coordinating with the Map Group. Keep in mind that you are able to comment on their blog, and they are able to comment on yours. An easy way to see what they are up to, and to let them know what you are up to, is to read their posts and comment.
Second, as you move forward, I think it would be worth talking some more as a group about what your mission as a group is. Unless you have a clear consensus about what you want to communicate to the listener, you will run the risk of (a) simply allowing the existing knowledge about Dowling, or the existing narrative that they will find on the markers they see, to stand unchallenged, without any new context or insight that they couldn’t already get from the marker; and/or (b) simply making your decisions on the basis of what’s most entertaining or least boring. Ideally, you will be able to come to a collective decision about what you most want to communicate to the listener, or what you most want them to get out of your walking/driving tour. Then you can decide how to meet that objective in an engaging way. If you decide what’s interesting or colorful first, before deciding on your objective, you may end up putting the cart before the horse.