I suspect I need to use the resolve() method on the Rectangle to get its location, and then use that when setting the textFrame's geometricBounds, but it keeps appearing far off the page.
Any insights or examples of how this could be done would be welcomed greatly!
I think there is no 1-line code solution.
I suggest to calculate a textFrame geometricBounds regarding to rectangle geometricBounds and create it with [y,x,Y,X] or move existing one to [x,y].
So it looks like mathematic effort.
maybe this script will be helpful (at least some its parts ) :
There are options Size > Selection and Content > Text, so you can select the rectangle you need and use the script. Or you can take some functions or blocks of the one. Unfortunately, all the comments there are in Russian
Yeap, using the rectangle's geometricBounds as the base for the new textFrame's geometricBounds did the trick. Thanks!