I know! I know!
It was homemade from McCall's pattern number 4405, dating from the mid 1970s, but it has all sorts of 40s detailing. I was lucky to have had the pattern for sale recently, and when I found the homemade dress I recognized it immediately.
[Gotta love those Farrah Fawcett faces on pattern envelopes of the era!]
BTW, the dress is currently for sale on eBay.