Airliners built by Boeing pre- WWII:
Boeing 247- low wing monoplane; all built for United; only about 70 built; all accounted for.
Boeing 307- low wing monoplane, first pressurized transport, only 10 built, all accounted for.
Boeing Clipper seaplane- also only about 10 built, all accounted for.
Boeing pre-war bombers:
Boeing XB-15- even bigger than B-17; one built, crashed.
Boeing B-17- all sold to US Army Air Corps.
By the way, a transport with seats removed is not a bomber- no bomb bay.
I have flown in a B-17 and it would NOT make a good airliner.