It’s not quite 80mm but close enough. The slots also are a bit bigger so this helps with the fit as you can see in the photo below. But basically, you are correct.
I would recommend going ahead with the design of your table but waiting to buy your materials until your Onefinity comes in. This would allow you to verify dimensions before accidentally wasting money. In my case I needed to verify my X-rail foot to foot dimensions to make sure everything would fit properly.