So, I've been messing around in the shop last few weeks putting this together.
I used some thick kydex and created a backer plate that wraps around the top of the k3 frame. Secured some pole hinges I found at a marine supply place with 1/4"-20 screws and t-nutz through some tabs that I folded over around the frame.
2" adhesive backed Velcro on either side of the kydex frame makes a landing for the Velcro on the k3 flap that would normally marry to itself.
Costco carbon fiber trekking poles with the ends cut off gave me just enough length to clear the bottom of the pack. Bonus here is I can unscrew the hinge with my Leatherman and use the trekking poles if I choose, as they're still long enough my preference. I had to sand the hinge nubbins down a little to get them to press fit. I'll add some epoxy to secure the pole half of the hinge, once I find the right adhesive.
Sourced a super padded seat from my alpz turkey vest and was able to thread the Velcro straps through the sliders on the bottom of the pack easy enough. Some shock cord tied to the pad buckles and cord locks zip tied to the frame make for an adjustable retention for the seat when it's flipped back. I messed around with some magnets to hold the seat up, but will wait till I get some field time in the setup to see if I don't like the shock cord.
The whole thing is pretty comfortable when seated, and the seat folds up and down easily without having to adjust the cords. It won't stay put if I'm not using the seat pad. Sitting on it crates an anchor for the whole system.
I can adjust the pole length clips easy enough by just reaching back and one handing it, but am a little worried that one of the clips will come undone and I'll lose a pole section in the brush somewhere, but whatever for now.
There's some flex of the poles at the hinge, which makes me question the strength of the nylon under torsion, but a metal one is proving hard to source. The nylon hinges should do for now. Flex at the hinge makes it easy to pivot in the seat to square up in different directions, actually a real dynamic feel I think this will help in using a rifle from the seat.
Bonus
I have been trying to make my mystery ranch mule bag work on my k3 frame for awhile now. By shortening the side straps and putting some double sided Velcro on them, I can get the lower ones to sit underneath the shoulder strap Velcro, which holds the sides in snug to the frame.
Some g hooks on the load shelf and top straps made the rest of the attachments adjustable and pretty easy to take on and off.
One of the things I'm still figuring is the k3 bag straps and how to make them work with other, non exo bags. I'm leaning towards just adding some slide stops to the k3 bag and eliminating the clickers, which would make the whole thing a little less cluttered, but don't wanna make that decision till I'm sure it will be functional. For now I've got some repair buckles holding the upper and lower frame straps to the mule bag. The sea to summit 1 inchers actually click into the exo female clickers good enough to run with for awhile.This makes a nice amount of room for my turkey hunting stuff and give me the option to carry something large in or out of the woods with some adjusting.
This pack along with my fhf chest rig should be a cool, flexible combo for turkey hunting this season. Stoked to get outside and try it out.