Hi - this may not be the easiest way or the best way to get art assets into dev kit but it worked for me and I would like to share it, since it has come up a few times.
I’m not a developer at all - I was just trying all the options randomly to try and get it to work. I hope it works for you 
I bought the modular Sci-fi hallways and interiors packs on the marketplace for help with the sci-fi elements of my ark mod - basically i want to take players inside the obelisks as part of a storyline thing, and I thought these looked perfect for that.
Trouble is the assets are engine 4.8 / 4.9., and Dev kit is 4.5 so while the brushes and textures would load (if i copied them manually), the maps wouldn’t.
I’m not a level designer so just having the brushes and trying to put them together is probably simple for other people but not for me - I had hoped to be able to get the maps in as well to at least begin with a template.
So:
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I made a blank project in unreal dev kit (4.9 engine), and a blank project in Ark dev kit.
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I added the scifi assets in the dev kit to my unreal 4.9 project.
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I loaded up the maps one at a time in the project, so that they ran in the window, and each time I selected “export all” and exported the maps as .t3d files. (unreal text).
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I then manually copied the sci-fi assets folders in windows to a sub directory in my blank ark project (the t3d files were saved inside the maps directory).
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I loaded my Ark dev kit project, and then I imported the .t3d (file>import) which looked for the assets in the directory hierarchy of the project folder… and loaded them up with out errors.
et voila… the demo maps work without any errors.
There are a few bits that still need to be done manually - like that I’m falling through the floor and whatnot.
For info my next challenge is trying to get the substance 4.5 plugin to work in Ark so that we can import sbsas files
I’m really loving the Allegorithmic atlantis demo and hope I can do the same as I did here.