I completely agree with Andy, and it’s not because we‘re both derivatives of Andrew.
If you’re still new with the AxeFX, I can see you causing yourself a lot of unnecessary grief by assuming you can take the IIC+ model with any 1960B IR and get the MoP tone from it. There’s a LOT of other variables in the mix, figuratively and literally. If their Marshall 4x12 was modded, how was it modded? Are the speakers the same? Even then, you’d have to find an IR that was basically shot in the same room they used, with the same mic and the same signal chain the mic had, and the mic would have to be in the exact spot they had their mics on. How broken in was the speaker they mic’d? Did they have more than one mic on that 4x12? Did they EQ the signal coming from the mic before or after it was tracked and mixed?
If even one of those variables are off, you won’t be getting the sound you’re looking for. You can try 1000 1960B IR’s and none of them can sound like the one Metallica used.
What I would do- make a preset as follows;
Input - Looper - Drive - IIC+ - Cab - Parametric EQ - Multiband Comp - Output
Keep the Drive, P-EQ and MBC Bypassed for now. The cab doesn’t matter too much yet. Load the Guitars Only mp3 or wav into your DAW as a reference track. Pick a riff from the song and record it with the looper so it’s playing over and over. Start tweaking the amp settings until you’re getting close to the ballpark. THEN go to your Cab block and start searching for a better suited IR. Since the Looper is playing the guitar part for you, all you have to do is focus on finding the right IR. You should be able to get about 85%-90% with just the Amp/Cab block. Only add in the drive/P-EQ/MBC if you need it. You might need to tighten up some low end, around 80K, which is what the MBC is for and the P-EQ is just for any fine adjustments you may feel you have to make. The Drive is just there in case you need to boost your input a tiny bit and get a little more cut from your guitar. The amount of distortion from the amp itself should be more than enough to get you where you need to be, but YMMV.
Going this route will give you a better idea of what’s going on with IR’s and how they sound wildly different from another. I could get one 1960B from York and it’ll sound entirely different than a 1960B from Ownhammer, it all depends on how they mic’d it and the signal chain leaving the mic. This will also give you a good deep dive in learning how to really tweak your presets to get what you want, instead of relying off an idea of what you want to get there.
Also, dig around the Recordings and Preset Exchange, I’m 99% sure someone already made some MoP presets. If worst comes to worst, you can always buy a pre-made preset and tweak until you’re content with it.