So what keeps the neck in alignment with the frame while welding it up? It seems like a 1/4 of a degree out of plumb up at the neck could really throw things off down at the bottom of the forks.
I noticed you have a large gap that has to be filled in. I assume you are reusing the factory neck? Any reason you choose this one over the HHI kit? IMO the HHI kit seems like it would give you a little better alignment tolerances.
the yaffe tubing is what keeps it aligned, we use a level to check before and after. On the first one we did (mine) we purposely reefed on it to see what would happen - didn't move - using the painters tram gauge to measure points on frame to neck (hes a frame straighten guy at work). the gap in center gets and around filled in with sheet metal, the pieces on bottom are about 3/16" thick. the oem neck is no more then thick sheet metal with a 2nd layer of sheet metal "folded" inside. As for the hhi, the cost is why we don't use it. not saying its better or worse - just the yaffe one works and very easy/quick to do and allows for custom stretches if they want it.