Thank you very much for the replies and explanations. That is reassuring, so that is what I'm going to do: drilling these bloody welded nuts.
And thank you for the tip about the stainless steel bolts. I hadn't thought of that, so yes, I will try to fond 12.9 grade dome head bolts. But of I can't, I can use Allen or hex heads as here in Sweden, we don't have the radius issues you have with your IVA. And the 12.9 grade bolts I can source are black, so it is even better for the look
Thanks a lot.