How do I keep a variable heading and paragraph together when flowing from one text box to the next?

That would be a nice feature, but I don't think it's possible to keep lines together in linked text boxes in PSM 7.

Under Window-Toobar select Text Formatting. Use the Link text box tool as follows:

To link text objects

Make sure the destination text object(s) to which you want your text to flow towards already exists.
Select the first text object.
From the Text menu, select Create Forward Link, or on the Text Link toolbar, click the Create Text Link button.
Point with the mouse cursor to the text object where you want your text to overflow towards (the destination object).

When you move the mouse over a text object which can be linked to, the border of this object will become green if it is possible to link to this object, and red if this is not possible.