This article covers the basic principle of changing a form field from a dropdown and will get you started:
https://acrobatusers.com/tutorials/change_another_field
However, the example is changing a set of text fields from the combo selection. Radio buttons are a little different, but not much. A radio button is turned on when the value of the Radio Button Group is set to the export value of a specific button.
So if you make the export values for the list the same as the export values for the radio buttons, then you can use this code in the Keystroke Script for the combobox
if(!event.willCommit)
this.getField("RadioGroup").value = event.changeEx;
The "RadioGroup" needs to be changed to the name of your radio button group
Thom Parker - Software Developer at PDFScriptingUse the Acrobat JavaScript Reference early and often