I'll try and help...
First you must get the flange angles adjusted correctly. This part has a flange that varies in angle around the part. At the top center the turtle deck skin meets the 807A at close to a 90 deg angle but moving around to the sides, it transitions so that the flanges are bent more than 90 deg to match the taper of the tail cone. The flange angle is constantly changeing around the part that is what can make it a little more difficult to adjust.
Once you think you have the flange angles close lay the part on the fluting diagram on a flat table and start fluting a little at a time at the marks until you get it straight. If you over do it in a particular area slightly flaten the flute to make it go the other way.
Less fluting will be needed at the top center than on each side because of the difference in flange angle.
If while fitting the turtle deck skin, you find you need to readjust the flange angles, you may have to also adjust the fluting slightly.
