Last night's update.....
There's a LOT of good learning going on!

I'll share a few "tips" that I've learned about header building that will help other novices who want to give this a try someday.
Rule 1: Bolt in your head flange AND get your collector spot tack-welded exactly where you want it. If you don't clearly define the start and stopping points for your tubes, you'll never be able to run multiple tubes simultaneously and land them with any amount of precision...
Rule 2: It seems to be easier to work from the ends of the runner and meet "in the middle" than it is to try to build in one-direction (either head flange to collector, or collector to head flange). This is especially true if you have a long straight section that needs to be precisely aligned like I'm trying for.... because:
Rule 3: Make sure that the "mock up" materials are rigid enough not to flex, and fit tightly enough that they don't sag out of position. All you end up doing is wasting time. Here's a perfect example of what NOT to do:
I was "sleeving" my collector with craft paper, and when the weight of my bends started to buckle them, I used old papertowel and wrapping paper rolls. But since they didn't fit snugly into the collector tubes, they still shifted too far out-of-position to give me useful target points to aim for with my bend sections.
The solution was to slice a few cardboard tubes lengthwise and then sleeve them together with the open seams at 180* opposite from each other. I kept adding sleeves until the fit into the collector was REALLY snug and it made a HUGE difference....especially when it came time to fit up the 2nd & 3rd primary tubes.
Rule 4: Work across the bottom of the collector first (#8 and #4), then work on the two top tubes (#6 & #2). It kind of makes sense to build the primary tubes that will go on the bottom FIRST, since you are unlikey to have a path to get down there once you add the two upper primary tubes. By placing the bottom ones first, you reserve the space you need immediately and whatever space you are left with becomes your upper primary routing spot.
Here's how the tubes ended up looking at the end of last night. The clearance around the strut looks pretty decent to me....
From this side-view you can really see the benefit of having rigid tubes going in to the collector area. In the previous photos, those tubes were drooping and sagging and I was getting nowhere on the design.
The alignment of the primary tubes into the collector ended up really nice and parallel... even though I was using cardboard. Once this is rendered in stainless, of course I can get this alignment even more crisp and perfect!
...and finally, a view from a few feet away to show the overall effect of the outboard headers!
It's hard to find a camera angle that really shows how cool all of the primary tubes look, but as you walk-around in person and look at the routing of the exhaust it is REALLY awesome and fun to see it snaking around and spilling out over the top of the framerail....
This exhaust project is turning out to be every bit as fun as I imagined it would be!!!
-G