I had a LT5500 on a K3 frame for a few years. It's easy enough to swap some buckles and make it work.
The only problem area i found was the top of the bag to the top of the frame. I ended up using gatekeepers for quick access to the meatshelf, but k-clips would be tighter. Most of the hardware i used came from milspecmonkey.
Also search for "franken packs" here. There's a couple old threads that have creative ideas and pics for attaching different manufacturers bags to unmatching frames.