I've always thought that the best way to begin a project is to ask those who have been there before.
I have a 914 here and some GT fenders to weld on. Being somewhat of a panel beater and welder, I'm going to use the typical methods, Clecos for mock up, panel clamps for alignment and a MIG welder to tack.
The only departure from what I've done in the past is that I'm going to butt weld the fenders using oxy/acetylene with a micro (or aircraft torch) and some ER70S-6 rod, which is very malleable post weld. I will dolly all the welds as I go before any grinding. If necessary, I will shrink as I go as well. From the best info I can find, this is how the factory did things like GT's and some of the 911 factory race cars.
I usually go over my welds with a light on the back side looking for pinholes and braze them. As further insurance, I use lead over the seem as needed to finish.
However, I know there are a couple of pitfalls to watch for and that's why I'm posting. I've seen some incredibly nice work here. I hope to be that best welds thread for 2009.