The new interface always uses a separate php page for the body. You can open that page and add recordsets and other dynamic data directly. If you want to reference a recordset from the page where the email is applied, you just have to declare it as a global variable on the top of the email body page like:
If you have a specific example of what you are doing I can help with the steps, but it depends on the data you are adding and what is on the original page already. Give it a try and send me the files if you get stuck and I can help you update them.