I'm sure I can figure out a way to mount the recessed I reclaimed, which are missing the bar hangers; however, does anyone have any previous experience in doing so?
Sure, just rotate them 90° and attach them to a ceiling joist with nails or screws through the bracket where the bars used to go.
Of course then you have no adjustment for placement between joists.
Why not just use lumber? Run two boards between trusses where the bars were, then screw the can housings to that through the vertical flanges.
I applaud your motivation to reuse hardware in this throwaway society. The financial cost of the product isn't the only cost. That steel and the work to galvanize and form it takes a lot of energy, chemicals, and water.
This gadget, the Caddy TSGB16, would probably work
with the keyholes in the plate in your picture.
edit: it's available for $2.12 online, may be available cheaper at a local electrical supply or industrial supply.