Well Alex
Since there were only two YC-30s, I suppose I have a 50% chance of getting it right...
Since they were coded '56' and '57' my logic (not necessarily USAAC logic...) says it is the first one 33-320 c/n 26 and delivered in May 1933. The other one was very neatly 33-321 with c/n 27
I believe it was a kind of Washington DC VIP transport and if I am not mistaken you have the Bolling Field insignia on the fuselage.
One was w/o in 1938 and the other I believe wfu the same year.
If you check Joe Baugher's site, he has hopefully more details (I have not done that, since I have to start preparing the dinner....
)
I also think I have more details, but my flat is right now a bit upside down so I cannot reach my written files. Sorry about that
Cheers
Stig