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Alright kc8gpd, I found what you asked about, a build-it-yourself FM transmitter with stereo generator. I found the instructions while paging through a file of old circuits.
This project was published in Radio Electronics, July 1992, and is a detailed circuit and 3-page article about building an FM stereo transmitter based on a BA1404 chip.
I hope you can find a way to trace back and find this, my scanner is out-of-service and I am not able to make copies.
It does not mention the power output, but the instructions describe tuning it up for maximum output to nearby radios, so it’s probably close to Part 15 compliant.