Multi Radius design

Working on a guitar design.

With the finger board, I have the 2d done, but am unsure how to proceed with getting it to 3d with the following restriction. It needs to be 1/4” tall at the center line, with a 9.5” radius at the narrow end and a 12”radius at the wide end. It seems to be really easy if it was a continuous radius all the way, just extrude a rectangle, draw at the end and eliminate the excess of the rectangle using the curve. But I’m unsure how to do it when the curve changes over the surface.

I would use loft to create this curvature and then subtract it from extruded body of finger board.

Or use loft to create body itself.

I agree with @Xdrakosha that loft is the way to go. Here’s a way that might work albeit a bit unconventional.

Here is my example

I’m not a guitar fan, so I’m not sure it should looks like that, but hope the conception is clear.