I used to own a 60s Ventures model Mosrite, and have played many of them. The pickups are hotter than Fender pickups, but not as hot as Gibson pickups. Other than that, you're completely right. I got to meet Nokie Edwards once, and he said the sound on Walk Don't Run '64 was created with that Red Rhodes fuzz, not the amp being overdriven. It's a very mild fuzz effect, you almost wouldn't even think it was a fuzzbox. I have never, in 20 years, been able to find a fuzz that would make that sound. And yes, he always used (and still uses) very light gauge strings. I honestly don't think there's anything really special about the sound of Mosrite pickups. P90 pickups will get you close enough. The earliest Mosrites (like the ones played by Joe Maphis and Larry Collins) had Carvin pickups, and those DID have a very unique sound.