So I haven't seen much on the net comparing the two purely on specs, more so on forums saying what people prefer. What all did they do different with the FA20 block in comparison?
I personally haven't seen any tear downs of the FA20DIT yet. Here's some Japanese media coverage of what goes in to the motor. I think the EGR system is slightly different for the USDM motors but I could be wrong. http://clicccar.com/2012/05/09/149871/ What questions are you wanting to be answered? If you're talking bore and stroke the EJ20 series motors are 92x75mm and the FA20 is a 86x86. They're pretty dissimilar motors other than both being flat fours. Here's a teardown of the motor in the BRZ which should be similar. http://www.revvolution.com/blog/2014/03/tearing-down-and-assessing-the-fa20-4u-gse