Patrick has sent me these three pictures of two metal tank models. They are approximately 3 inches by 6 inches, and seem to be an M3 Lee and M4 Sherman 105mm.
(It has now been persuasively suggested to me elsewhere that the Sherman is not the 105 mm version but the T6 Medium Tank, i.e. the Sherman prototype. The photograph below is of the example built at Aberdeen and I think confirms this identification.) There seems little point in having identification models of the prototype much beyond 1942 when the production models were introduced. As the lee was also introduced in 1941, and there are clear similarities between the two models (the running gear), perhaps these could even have been models used as part of the prototyping process?
Patrick (and I) would be very interested in and grateful for any information on their likely manufacturer and date of production.