You can think of this as two right triangles with angles of (8 degrees 27 seconds)/2= 4 degrees 13.5 seconds (There are 0 minutes? I want to be sure you didn't accidently say "seconds" when it should have been "8 degrees 27 minutes".)

For "x" feet, as measured along the axis, the width will be 2(x)(tan(4 degrees 13.5 seconds)= 0.1400 x. so the taper is 0.1400.