Try to keep this as short as poss. Have done this deal and it's a bit tricky....to get it right. First off, most outers are repops. Second, you may be applying another repop ie 1/4 panel, 1/4 skin. To verbally illustrate a major pitfall, Do NOT put the wheelhouse on without measuring the radius of each piece. I did a 66 cv that was someone's never completed project. They had removed the 1/4's. A guy at a shop had put a new wheelhouse on one side. So, getting repop 1/4's, quickly discovered that they would never fit together without fitment issues. Each radius was a bit different.For all I knew the wheelhouses were made on mainland Chinca, where the 1/4's could have been done in Tailand. This entire job took a couple weeks as I walked away from it to do other things and there was no hurry.
Bought 2 new wheel houses. Cut 2" off the one new and remaining original outer wheehouses. I then cut 3" off the new ones. With a LOT of vise grips, tentatively attached the new 1/4 to the car. It's important to do this so that you can get the gaps and looking down the side of car, see if the 1/4 is not out to far at the wheel opening. Next step is to attach the new 3" piece to the 1/4 (slid these in and attached it to the stationary Wheelouse). Joined the new pieces to existing wheelhouses with a few tec screws around the perimeter. When you are sure that all is lined up, etc. remove the clamps/grips attached to 1/4 and remove it.
Now....you can weld the new piece of Wheelhouse to the existing one. You can then finish off the wheelhouse like new and shoot it body color. Those who have done color changes on a Mustang know that this is an area where getting original look coverage is about impossible.
When doing the entire back end of a 66 cv, I also shot the backs of the 1/4's, after first replicating the indercoat that factory did. When assembled, your car will look like it was never painted.
Not sure how many1/4's you're doing, but I roughly assembled the entire back end, including tailite panel(orig Ford!) with the aid of tec screws and Vgrips prior to final welding. Was able to loosely fit the decklid and get gaps right. And important part, also, was marrying the lower 1/4 to the rear valance.
If you are doing 1/4 skins, every 67/8 skin have seen is not the same as the 1/4. The original and repop full 1/4's have a recessed area at the lower rear allowing the valance to fit flush. The skins do not have that recess, at least the ones I have seen. It will be difficult to get the valance to flush fit with the 1/4. The valance has a bracket to house the attaching screw while the skin doesn't. That bracket could prevent a good fit.
To summarize could have possibly left the new outers intact. One reason I didn't was the convertible outer has a flat surface at top while the repops don't. It just didn't seem like the best deal. Would do the same on a fastback trying to save as much of the original as possible.
Hope this helps you. Others may have a different approach, this one worked for me.
A sidebar to this job. The cowl also was terrible and discovered the hinge pillars needed replacement, yet the floors, framerails, tboxes were solid! Go figure! LOL!
[This message has been edited by mellowyellow (edited 06-05-2006).]