Look for GSpread.NET. It's also an OpenSource project and it doesn't require Office installed. You can work with Google Spreadsheets by using API from Microsoft Excel. If you want to re-use the old code to get access to Google Spreadsheets, GSpread.NET is the best way. You need to add a few row:
Set objExcel = CreateObject("GSpreadCOM.Application")
// Name - User name, any you like
// ClientIdAndSecret - `client_id|client_secret` format
// ScriptId - Google Apps script ID
app.MailLogon(Name, ClientIdAndSecret, ScriptId);
Further code remain unchanged.