I would either damp spray cellulose or install the interior drywall and then blow it. Problem is that you are doing it blind but if well documented before drywall, it should still be able to be done properly.
Thanks to all that replied. It is an exterior basement wall. We don't get to decide how it is built, we just get to insulate it. We have decided to blow these cavities after the drywall is hung. They are installing 2" Blue Board against the foundation then installing steel studs 1/2" in from the Blue board. We will blow these from the top or use a hole saw to cut through the drywall and replace the plug if necessary.
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