I've done loads of these over the years, both genuine panels and non genuine.
The way I did it was:
1. Repair the doors and a posts
2. Fit the a panels, set the door gaps and weld the a panel top and bottom so its fixed.
3. Bolt the front panel to the subframe
4. Fit the bonnet and get the gap as good as you can at the back.
5. Position the wing and tack the rear corner by the bonnet and front corner by the bonnet to the front panel to set the gap by the bonnet. Repeat for the other side.
6. Pull the wing to the a panel with mole grips with a wide head.
7. Recheck the bonnet gap.
8. Weld the wing to the inner wing along the top.
9. Weld the apanel to the wing.
10. Weld the front panel ears to the inner wing.
11. Clamp the front panel to the wing and weld, working your way from inside (nearest the inner wing) to out tends to help.
12. Dont forget the little angled strengthening pieces welded to the wing lip where it joins the apanel which add quite a bit of strength to the joint.
If things aren't going right then stop and take a step back, sometimes you get a bad panel, sometime moving something slightly makes a big difference to the fit elsewhere..
It should be possible to get a reasonable fit even with patten panels without major reworking, if you have to cut panels up and extend or shorten them chances are that either the panel is wrong made or your trying to achieve a far better fit than the cars had when new.
The last point above is important as these cars had poor gaps from new and try to get them perfect is a time consuming and generally unnecessary endeavor, to top is that the gaps are more critical on light coloured cars than dark coloured ones. Dark colours hide panel gaps but show dents more!