I just realised you asked about the radio button. there's a couple of ways you can do that.
(I've been talking about the select, only.)
Set the option values to your select dropdown to equal the possible values of the radio button.
Then do one of the following:
- make the radio button and select value use the same name (the name="attr_whatever" part) - they can be the same, even though the HTML elements are not the same (radio and select).
- Have a sheet worker that detects wehnever the selet changes, and saves its value to the radio button