Re: Pickup help
First thing to understand when trying to make one guitar and any amp+pedal sound like anything on a CD you've heard (i.e. Metallica's guitar tone) is that the CD tracks have been doubled, and layered, and they're mixed with other layered and doubled guitar tracks, as well as the bass and drums.
All that contributes to the sound you're hearing. It's not just one guitar+one amp. It's not even James and Kirk with a guitar and amp each. What you hear on the CD is not what you'll hear standing in front of their amps, either. What you're hearing is a processed sound tailored for most CD players and radios.
On top of that, it's been widely reported that Hetfield used a Gibson Explorer with an Invader for Master of Puppets. It's also been widely reported he used a Gibson V with an Invader. And an Explorer with an original Gibson Dirty Fingers. And a Gibson V with a Dirty Fingers. And a white Jackson King V with a Distortion, Invader, or Dirty Fingers.
I've not seen anything where Hetfield himself said what guitar+pickup he used, and on what tracks. However, I do know that an Invader in a Jackson Warrior through my rack into my PC+studio monitors sounds close enough to Master of Puppets on my CD player.
But then I've got a ton of EQ in my rack so I can sound like anything I want.
The point to all that is that it really doesn't matter which pickup you get - Invader, Distortion, Custom, JB, Screamin Demon, Full Shred, Fred, Evolution, ToneZone, SuperDistortion, Hot Rails, etc etc etc: it's going to take more EQ than anything, because what you're trying to match is a studio-processed sound, so save your money for a decent EQ pedal. The MXR 10-band graphic should work just fine. A cheesy little 5 or 7-band might not have the frequency control you need.
And a noise suppressor/noise gate to control the feedback.