I get as many American Car mags as the budget will allow (too few these days).
I get CarCraft, Hot Rod, Popular Hot Rodding, I loved Circle Track, until Smokey left, Open Wheeler, the various 4WD magazines, Guns and Ammo etc.
I find the American magazines to be technically far superior to the advertising brochures that are available home grown, and from Europe these days. The last great bastion of technical innovation died 5 years ago, when an Australian Rod magazine was publishing a set of articels on running chevs on propane (22MPG US from a 350), and the readers demanded that it be removed so they could show more cars.
In short, there are a heap of technically worthy American Mags available. And given your market size, every single one of them can be "niche", as there are enough niches to keep 250 million people entertained.
If you don't like the articles, in Hot Rod, pick another Peterson publication that deals with what you want.
Didn't they have Dobberton's J2000 in Hot Rod ?