First off, where is Lumby? It's not a place I'm familiar with. Secondly, the brake backplate is definitely structurally deficient. What my tests found is that, at a certain point in brake lever travel, any further force applied or lever moved doesn't increase the force on the brake shoes - it all goes into distorting the backplate.
Frankly, I've never seen the stiffener kit, so I can't be absolutely sure that it fixes the overall problem, and the photos of the brittle-lacquer testing are probably long gone. I wouldn't think the longer actuating arm would help without the stiffening kit, as it was distortion of the backplate that was the fundamental problem.
Long-term, putting safety above originality, I'd be tempted to go with one of the many post-production disc-brake conversions. Yeah, they're not cheap, but being able to stop in the next 5 seconds, rather than sometime today, maybe, definitely has its good points.
The purists/concours specialists that want to see everything kept as the factory originally delivered must not be regular riders. The Commando is too good a basis for updating as a reliable daily rider to get too wrapped up in "originality". A lot of the enthusiast modifications I've been exposed to on this forum would have made the bike a world-beater if Norton-Villiers hadn't been so skimpily funded and stuck with top management so divorced from motorcycle realities.
I put in a proposal during my last few months at N-V for what turned out to be a Gold Wing, though I had no idea Honda was thinking that way. Shot down in flames because there "was no money for that kind of pipe dream!" (and I think I was too far down the pecking order to have any credibility).
Such is life, I guess.