I have a very specific need. What CAD should I use?

I want to make a brass stamp for doing gold leaf on book covers. There's a guy in the UK who can do it for a price, but if I have access to a cnc mill why not do it myself? Technically all I need to do is extrude my image from a solid block, but ideally the surface of the stamp should be slightly curved, so you can get a sort of rocking motion in. What cad program can i use to add a curve to an extruded shape, and how would I do it? I'd also need to add a bevel, for millability.

Maybe openscad and a minkowski with the surface and a cone? Example with two cubes:

minkowski() //What it looks like is attached.
{  union()
    {  cube(size=[10,10,10]);
        translate([5,5]) cube(size=[10,10,10]);
    }
    cylinder(h=10, r2=0, r1=5);
}

For the look of the stamp.. I don't know, maybe use these tables? Or do something with dxf files?

Ftr: this thread contains two solutions to getting pictures into designs. (Though it sucks in some senses, I prefer mine)

My problem isn't importing the design. It's a vector graphic so I just save it as dxf. My problem is how to curve the flat logo and then extrude it inwards. I considered extruding it as normal then cropping it with a sphere to curve the working surface, but wouldn't that give it a fisheye effect? Or do you think it wouldn't affect it that much since I'm only curving it slightly?

If you printed in two pieces, the first a very thin layer (perhaps .5 mm) with the print atop, then a stamp "blank" that had the required curve, you could laminate the first print to the second. If ABS, the weld is easily done with acetone. I * think this would retain your geometry without distortion...I think.

Alternatively, if you can push the embossing area through a cylindrical lens effect first (rather than a section of a spherical window function...you'd want the distortion only in one dimension), you can do the print as a single entity, although I'd question how accurately that approach would be for detail in the embossing area.

Intersect the extrusion (assuming that, when you say 'extrusion', you mean that the vectors have been thickened, shelled or offset, depending on modeling SW, so that the artwork extrusion has volume) with a sphere, then apply chamfers to model blade edges. G-code is generated from the model, as with reprap printing.

Unfortunately this doesnt work.. For some reason CGAL doesn't get the intersection right..

sphere(30);
intersection()
{ rotate(a=90, v=[1,0,0]) multmatrix([[1,0,0,0], [0,1,0,0], [0,0,1,0], [0,0,-0.1,1]])
        translate([0,0,-1]) surface(file = "round_stamp.dat", center = true, convexity = 1);
  sphere(40);
}

I guess one could try apply a function on the height map to make it round.