jlloydpark,
Welcome aboard. I would estimate the basic lathe as having been made in 1947. The QCGB was added within the next 3 years or so as from the shape of the tumbler lever, it is the early version. And if it had been bought with the QCGB, the model would have been QC54 instead of TH54. I would recommend adding an oil drip pan between the lathe and the cabinet top. And if the lathe has seen much use, you may not be oiling it enough, as the wood top shows no signs of ever having had oil dripped on it.