You are on the right track. No there is no rule that the top flat must be t he same width front to back. I'd suggest making them a bit smaller width at the front, tip end and a straight taper from the barrel cylinder width. Even just a bit thinner will allow a more rounded forend.
One caveat about the Fisher drawing, They are Wonderful, But the given dimensions are different that taking measurement off the drawing.

Last edited by SDH-MT; 05/04/25 05:09 PM.