I know you are talking a 1934 but one thing I did on my vette to trace it down was to pay CARFAX. I dont want to sound like a rolling billboard for them but they did list all the owners for the car since new ... maybe it can get you a few past owners on your car, but considering the age I dont know.

On my 59 Sedan Delivery I have it traced back to 67 and that guy is working on the name of the guy he bought it from .... I'm almost there.