ChrisB, if you add one leaf to each rear spring of a 1967 Camaro, I found that it would handle a 427 quite nicely. But I never towed my race car faster than 120 mph.
Mini magazines: Darned if I know why there are so many problems with modern manufacture. I had quite a few after-market mags back in the 1970s/early 1980s. They always functioned properly. I never had to do any adjustment of the feed lips with needle-nosed pliers...