IF this was one of the Export letter cars, that could make it a bit more valuable than if it was a normal North American car, I suspect. No shots of the instrument cluster to see if it has a kilometer speedometer rather than miles?
Considering the time and $$$$ to "restore" it or at least get it road worthy, such activities would need to be driven by "labor of love" rather than economics. Saving the car from further deterioration.
Although it might be more expensive to restore it as a "K", that extra expense might be minimal compared to just restoring it in ANY fashion (correct 300, letter car, or "ratty"). So, making the investment would be viable, to me.
One main issue could be sourcing the cable-operated TF, a correct 413, and some trim items (which might be in the pile in the trunk). I don't recall if the K had a console TF shifter or if it was push-button. It's been a while since I was concerned about those things. Having a console shift could uncomplicate things, I suspect.
One alternative could be to do the needed body work well, get it ready to accept its new powertrain, refurb the trim items (not the upholstery), and then sell it after the "heavy lifting" items have been done. DOCUMENTING ALL things done as they are being done, for the new owner.
From there, the 413/360 was a single 4bbl engine with a hotter cam. No problems. AVS2 750cfm with a vintage Edelbrock 4bbl (1968-style) intake. Hide an electronic ignition in the mix, too. Then, under correct valve covers and cyl heads, sneak in a 440 with a 440/375 cam in it. Do some clean-up of the ports and such in the heads, for good measure. Keeping everything looking "as produced" in the process, covered in the appropriate Chrysler engine paint color. Although a real 413 block might need to be used if there are any year-specific motor mount issues as the 1965s had.
As to brakes, might need to find a rebuilder that can do some modern-friction linings on the existing brake shoes. To further enhance the OEM braking performance, rather than go back to what it was when new. Some might disagree with this orientation, but it would be easier than installing front and/or rear disc brakes (which might be an issue for later owners!).
So . . . incognito upgrades which can make the car a better performer and enjoyable driver, rather than an over-restored "don't want to drive it" museum piece. To each their own, just not "ratty". Keeping the car more-correct will protect its ultimate and continued value, by observation. Whether a normal "K" or an export "K".
Just some thoughts and observations,
CBODY67