Bit late into this thread but was a bit confused by the title.
Surely the Washington was the B-50 and the B-29, the Superfortress. It certainly was when I was spotter in the middle 50s.
The main differences were increased fuselage length, of course bigger engines and a substantial increase to the size of the rudder.
I instructed with a chap who had flown them in the late 50s, who later converted on to Valiants at Gaydon.
Can somebody confirm or disprove ?
Thanks.