moe-idk

I know there are many discussions about this, but I can't find a solid answer to my question. Can I only upgrade my rear sliding calliper to the amg 4-pot caliper, or would I need to upgrade the fronts as well? Also, if rears only is an option, would it be a direct swap or would I need extra hardware? Thanks in advance.

Chevota

I can't imagine the car would care, or know, if you did the front, rear, or both. That and you just might be the only one doing it so maybe that's why nobody can say yes or no? I think your only concern would be the obvious, which is; does it bolt on and do the parking brake cables match up and work? I don't use the parking brake, but maybe one day I'll have an emergency, so if given the option I'll take 'em.
Then there's the question of piston area. I'd imagine the four much smaller pistons are pretty close the area of the one huge piston you have? Maybe a little more because why not, it's AMG.
So if you changed the back, and the new had 10% more area, then it would apply 10% more force which would make the rears work harder and front less, and pad wear would reflect that. Might be for the better since rears usually last much longer

I am curious why? I get it if you just want 'em, or like the look, but if that was the case you'd most certainly want the front more than the rear, so I'm a bit confused. Function wise the oem brakes seems pretty good to me. I'd take the four-piston version if they were free, but I wouldn't actually pay $ for them since I don't feel a need.
My brakes are the original with ~75k on them, and I've been pretty hard on mine of late because I bought a new brake set ten months ago. So A; I don't care about these and I trash things I don't care about. B; apparently I need to wear these out to force myself to install the new ones. It appears they're bionic brakes because they seem unfazed by my abuse. I hit them pretty hard last week, at 120, and hard enough for ABS to kick in. I also felt no fade or anything negative at all, so that's why I consider them good enough as-is.
So if they bolt on, and you just gotta have 'em, go for it.

Chevota

I suppose I would start by looking at pictures of each, if you can find them. To see if the mounting and what not is obviously different. And I forgot to mention the disc diameter. If the AMG have bigger discs, and why wouldn't they, it's an AMG, then you might be screwed right there. Or maybe the mounts are the same and the caliper itself is positioned for a larger disc. Or maybe the mount is what's different, and pushes the caliper out further on the AMG? So many questions, I see your dilemma...
When I was a kid I'd hit the junkyards for "will it fit" questions, but junkyards these days post pictures of parts online. I look for parts on ebay, and those boneyards typically post many pix of the part from various angles, which is super helpful. Maybe that will be your yes/no answer?

moe-idk

I found some for a very good deal and just like their look especially since I got 19' wheels. As far as I'm aware they just bolt on with the parking brake cable needed to be switched for it to work. The rotor size on the rear I'm pretty sure is the same as e63 owners use e550 rotors to save money. The reason I don't want to do fronts as well is two-fold. First I feel that the brakes are adequate as you said, and second I'm fairly sure the fronts don't just bolt up and need a different knuckle. Based on what you said I think I'll see if I can secure these rears and just find out if they fit.

S-Prihadi

Do your research using EPC and a known VIN of donor car and your car.
If without VIN and using only chassis code, the EPC data is a generic one and could lead you to mistake.

You then compare the wheel knuckle P/N on both cars. If wheel knuckle the same, you are good.
Disc rotor size dictates what caliper size fits, if for rear wheel there is the parking brake drum assy which if you track by brake shoe replacement kit, you can tell if they are the same or not