I did exactly what you are asking. Here is my experience with pictures.
1) My original front trunk. Cut for A/C. Crumpled. Rusted out at the suspension points. CRAP!
2)The replacement part, cut from another car. Post up a wanted add, or bug someone with a parts car and you will find one right quick.
3)Drilling out all the old spot welds, and making my initial cut to remove the bulk of the original front trunk. In this pic, there is more cutting to the fuel tank wall left to do yet.
4)I still have to drill out the spot welds on the front, but the old metal is almost all out.
5)Lots of welding later.... All I need to do is add seam sealer. FIN!
This project represented my first go with sheet metal welding. From start to finish, it was probably 40 hours of work, with me learning what the hell I was doing as I did it.
Zach