If you think it doesn't exist, just keep looking!
Back in 2010 on a trip to the Strasburg Railroad Shops I came across this unusual marriage of RGS #20's tender and a six wheel standard gauge passenger truck. When you are rebuilding a tender frame, where do you but the tank? In this case it saved space and provided needed mobility for the shop staff.
Some guys have models of in-service locomotives with weathering very close to the appearance of that tender. We need to issue citations to such people. -- Russ
in the same spirit