A certain DIY project is starting to take shape.

The answer is it depends, Here is a simulation of a filter I used for getting rid of RFI. As you can see it acts as a lowpass up to 150MHz where after a dip attenuation gets worse. The dip is caused by inductors SRF. It could work in your situation, it has more than 60dB att. around FM band.

Turns out that the cheap USB-UART converter always reads back just a single byte. Second capture is with its TX and RX shorted, and somehow only one byte comes through.

Obsolete hardware✔️
Obsolete software from sketchy site✔️
Undocumented protocol✔️
Refuses to work for some unknown reason✔️
I *love* hobby projects with old industrial stuff.