Has anyone actually reported a crack, unusual directional wear, or bent hardware?
I was initially concerned that the aluminum bushing that supports the bellcrank would wear, but I'm not aware of that ever happening. However, I am aware of a couple of cars in which the 2" x 2" tube that supports the bellcrank developed cracks on the joint with the front billet upright. The other end of that tube has a large gusset which supports the toe link and the lower tube doesn't have a bellcrank so IF there is going to be an issue, it's likely to occur at the aforementioned joint.
These were endurance race cars which had more hours that the championship SL-C. On one of the cars, the cracks were detected during a routine inspection after 180+ hours of racing. Like the championship SL-C. they were running wide slicks (i.e., 345 mm), stiff springs, lots of downforce, and the rear sway bars were connected to the bellcrank. Curbs were ridden and there were a couple of off-track excursions. These types of loads will never be seen in a street car or someone doing track days.
The only thing that you shouldn't do is to cover the weld joints with heat reflective tape.... it will cover up any cracks that might develop.
The support arm is not required for a street or track-day car, but it's easy to fabricate and, other than the one made from right-angle aluminum, all of the above approaches look like they would work. That said, if you're going to the trouble of fabricating an arm, I would replace the provided top misalignment spacer with one that's welded to the arm.
Gussets appear to only be warranted for endurance racing or for nut jobs like me. Adding them is conceptually simple, but it's a lot of work given the amount of heat required. You need to strip the engine compartment to prevent things from getting damaged and I recommend fabricating a steel brace to connect the left/right sides of the chassis and temporary spacers to replace the bellcranks to reduce the potential of warping. I posted my approach here: (65) S2's Build Thread | Page 32 | GT40s