Does the 1958
Traveler have a gray tank under the floor?
My guess is that it does not. I can't really tell from the one exit pipe under the belly pan, which is under the toilet area. I suspect that if it did have a gray tank there would be two gate valves. There is only one PVC elbow from the bottom of the belly pan, with no gate valve (most likely broken off. Unless the original toilet had a dump valve inside for an internal black tank.
If there is no gray tank, then I will have to add one for an upgrade.