You might consider a hybrid. Purchasing an off the shelf aluminum unit from a more main stream agricultural company such as CM or many others.
Then add the lower boxes from someone like SET at a later date. You can buy them one at a time, and there are different size options. See fenders or tool boxes in this link:
https://setoverland.com/tray-accessories/
I purchased a full system from them, but noticed this option when doing so.
If you went with front and rear tool boxes, you could probably omit the fenders and have a near same effect. If your bet is short, then you'd probably only need the rear boxes anyway.
I have not seen plans for aluminum boxes, but there are plans for sale online, with video step by step instruction to support them, if you want to go that route. I don't think the aesthetic is quite the same as overland, but could be modified if going steel. Here is one such company:
https://ddfab.co/gallery/. No affiliation with them, just bumped into them when doing research many moons ago.
FWIW