Tina,
Sounds interesting.
1. What state do you live in? You might be able to access 1930s aerial photos of your area, to see whether there was a house or other structure standing on the front of your property, where the dip is. In Pennsylvania, ther is a website called Penn Pilot, where you navigate to your location, then select the period for aerials, then download the one closest to you and look at it in detail. In Delaware, they are at the SpatLab (Univ. of Del Spatial Data Analysis lab), but not well indexed, so the Datamil website is better - like PA, find your location, then select the period photo to download.
 
2. Here in Pennsylvania, there was a cultural tradition of houses with two front doors, one for the men and one for the women. I'm not at my office, so can't look up any references offhand. But my point is that you should not assume the two halves were built at different times, based only on having two doors. Is there other evidence that one half is an addition and one half the original smaller structure, or not?
Meli Diamanti