Lets get to cutting....

Ok so obviously to get started we need to remove the Miata front end. 

I'm not changing anything on the Miata in the center of the car. The doors will stay as they are. So what I need to do is make the Roadster fenders mate with the  Miata doors. So I am going to be combining Miata fenders with Roadster fenders. 

The Roadster fender test fit:

As you can see the core support of the Miata, as expected, will have to be cut for the Roadster fender to fit the Miata wheel well correctly. As you can also see the Roadster fender is more straight down at the bottom where as the Miata fender curves in. We will have to cut the Roadster fender right where the Miata fender starts to curve in.

So after removing the Miata core support and cutting to get the Roadster fender to sit back far enough, we can get a good idea of where we need to cut the fenders to mate to each other by laying the fenders over each other and using the wheel arches as reference. 

First I drew a rough line of the area we need to save on the Miata fender leaving more than enough room to trim as needed:

Cut it with a cut off wheel:

Then I overlaid the needed portion of the Miata fender on the Roadster fender using the wheel arch as reference:

Then I also cut the Roadster fender with a cut off wheel after I marked where I needed to cut making sure I leave enough metal for the fenders to overlap:

I then bolted the cut Miata fender to the Miata. As I did this I took the Roadster fender and overlaid it on the Miata fender. I positioned the Roadster fender where I wanted it on the car (again using the wheel arches as reference) I then laid the roadster hood on the Miata, centered it, used tape to temporarily hold it in place. Using the hood and wheel arches, I tack welded the Roadster portion of the fender in place while also using a level on the bottom lip of the fender to make sure everything was sitting straight. Once both fenders were positioned where I wanted them and overlaying each other I then used a cut of wheel and cut exactly where they met and stitch welded them together. The result was this:

(Passenger side shown)

Both sides tacked welded into position and leveled off. Double checked for symmetry and proper alignment:

Next is time for the core support mock up.