I was able to adapt Quan Tran's code from https://world.episerver.com/forum/developer-forum/episerver-forms/thread-container/2019/1/customize-multiple-choice-form-field-value-separator-/ and switch the string to boolean. Still waiting for the client to confirm that Salesforce looks correct but this seems to do what they want.

                    // get the selected value from submission data
                    var selectedValue = marketingActor.SubmissionData.Data[fieldName]?.ToString();
                    if (!string.IsNullOrWhiteSpace(selectedValue))
                    {
                        //replace string with boolean
                        if (selectedValue.ToLower() == "true")
                        {
                            marketingActor.SubmissionData.Data[fieldName] = true;
                        }

                        if (selectedValue.ToLower() == "false")
                        {
                            marketingActor.SubmissionData.Data[fieldName] = false;
                        }

                    }