Another bomber with comparable service life is the Tu-16/H-6. It was the direct competitor to the B-47 and new models are still rolling off the assembly line in China.
Were I to commission a bomber in the 1950s optimized for longevity, I would adopt a super-sized Avro Vulcan, in the range and payload class of the B-52. It would have two rudders instead of one and include some basic radar low observable features, which the plane form is well suited. The big delta wing is relatively cheap to make and maintain, and it would could transition from high and low altitude missions requirements with little difficulty.
One of the underachieving bombers of history was the Soviet M-4 Bison. Had it adopted the Vulcan plane form I believe it would've lived up to expectations and the Tu-95 would have never been needed.
D'oh. You are right about the Tu-16, which I meant when I typed Tu-26.