Back onto something of substance today. I bought on ebay one of those GRP dashboards with the IVA curve at the bottom but it never turned up so I decided to make one out of the spare half hard ally I had.
To get the IVA curve I riveted the bottom onto some 36mm water pipe and rolled it round With the thickness of the ally and the spring back I get a 40mm diameter, so 20mm radius.
I had to do this in smaller sections. You could probably do it in one if you have 2 people and a metal bar to rivet it to but I have a break in the middle of my dash anyway so you wont see any joins.