“Frankenpack” (search it, really) is a fun concept and I’ve done a bit myself but this definitely is not a straight forward setup. You would have to change buckles at a minimum and it likely won’t slip over the top of the frame without modifying the bag (it will be in meat sling mode all the time which is sloppy when not packing anything between bag and frame).
If you’re building a pack from used parts in the classifieds I would just find a kuiu bag, or exo frame.
If you really want to give it a go buy buckles from kifaru or the type they use/sell as it’s a widely used style making your project more future proof.
The problem with the KUIU system, compared to the others, is their utilization of 3/4" webbing where everyone else uses 1". You could still put a 3/4" strap through a 1" buckle, but it might not work as well, could slip. I'm sure you can find the Duraflex buckles that Exo uses online for a fairly reasonable cost.