I think Matts right about the alloy rivets, however I would go for Monel rivets. I've always used Monel, easier to work with than Stainless, in terms of, having to replace (easier to drill out)

I've had my boxes and blades since 1993, no problems with loads or the alloy block causing any damage. However, your rudder appears to be getting damaged by the stainless plate when locked down.