SEVEN: 外径长宽 30厘米X20厘米
BJG: 310X200mm

You might be able to get them to make it at a specific dimension though, but the fact your current ones is shorter means you still might be able to swap.

As to the boxes, the reason I like the BJG boxes better:

1) 25% cheaper

2) BJG has metal hinge, SEVEN is plastic hinge <- this actually surprised me! *BJG Top Box has a plastic hinge too!
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3) The BJG box relies on an aluminum lip with a rubber seal for the water-proofing whereas the SEVEN box is plastic on top and bottom. The bottom has a "ridge" and the top a "notch". I suppose they both seal well, my fear is cracking the plastic. In addition the plastic trim is seal with some kind of adhesive to waterproof itself to the box.
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4) The extra plastics on the corners of the SEVEN boxes. I'm sure they'll assist in protecting the aluminum, but I'm not sure if it's worth the extra dozen rivets that could potentially sacrifice water-proofing and would be hard to replace in the event of a break.

Either way, I'm sure they're both quality - and they actually seem fairly similar in build quality and craftsmanship. Also, if you're looking for a top box the decision is easy- SEVEN doesn't make one ;)