i'm using a Tubus rear rack on a mountain bike frame without eyelets - and i can't remember where i read this but Tubus says that the maximum load is now only 20kg at best for me, for my combination of the Quick Release adapter set with the Tubus LOCC, down 50% from the max 40kg that the rack alone was rated for.
The key thing you might want to specify along I might sound dumb saying this... is to ensure you have minimum 2-cross spoke patterns and an experienced wheelsmith building your wheels.
Good luck!