I found this listing of 10E and 10ER Serial Numbers in Everett Davis' Google Drive. He has a whole folder devoted to 10E and 10ER info. His thread is entitled "Shopsmith Large Format Drawings, Illustrations and More", and is one of the first three threads in the Maintenance and Repair Forum. It and the other two "stickies" (because they always stay in the top three) are highly recommended for new and old members alike.
Based on the first model reportedly being number 1001 (not counting the models sold in Australia), yours may have been built about 15 months after that, or early 1949 (SWAG)
10ERsurvey by Serial modified by Everett L Davis.pdf