I figured this out on my own today. The answer is to use a context variable for the parts, then feed the context var to the Response Body. The screenshots below show this:


Using the context var above, the gateway now responds with what I want:

I am thinking the "Save Line Breaks as: CRLF" was the culprit here. The Response Body in the GUI is not using CRLF at the end of it's lines.
-Rob