Been off chasing other bits of life. Thanks for all the ideas to think about. For those considering getting in to Gangster gaming, I went with the Blue Mooon 15/18 mm range for figures and buildings (bought all of there range with a few doubled up) and then sourced vehicles from various ranges from WWI, SCW, even a few WWII 'old looking' items, plus the rare appropriate matchbox type toy vehicles. Oh, I also have the Khurasan police and gangster figures and the Rebel Miniatures figures (that I belive started life at Splintered Light Miniatures).
Even though I bought all those 'Chicago' buildings, I suspect I will focus many games on events similar to the gun runners seen in A River Runs Through It (if memory serves). Essentially games where the Hooch is coming across the Canadian border into the US. Can have either rival gangs, cops, or feds involved - or all of the above.