I saw theXC-99 in the 90s at Kelly Air Base, San Antonio Texas.
It was in a sorry sad state, not sure if it still survives.
Dismantled and shipped to Wright Patterson for restoration.
The extra pods and engines were a straight kift off the B47 inners.
In the early sixties I was talking to somebody who used to fly them and apparently they had severe problems with propellor icing in the descent from high altitude.