That *sounds* like it may be a re-wrapped CS130D alternator to get that sort of power and still be under the hood on that V6 Malibu. Trouble with re-wrapped alts is that they tend to not generate high enough internal voltages to keep amp output up there when needed at idle with heavy accessory loads. They usually will not tend to hit max output until they hover around 2000 RPM at their rotor shafts.
Will it do what you need? Certainly. Will you be happy? More than likely. But let me seed your mind with doubt and see if I can light your amateur garage tech enthusiasm a little bit. :D
I'll be gentle...
For about $250, you may be able to find a rebuilt-to-new and beefed up stock GM AC-Delco alternator to fit your application that will more than meet your needs. Look into whether or not your current alt harness is compatible with a GM/AC-Delco AD244. (Adelphi Units are Decotrons too and are totally 100% swap for parts-n-all compatible)
They will hammer out a steady 100 amps for the asking AT IDLE when HOT, and do it all day long without trouble. All alternators work much less efficiently when hot, this one's just tougher and better at it's job. A junkyard pull from a GMC Yukon, a wrecked 2006 Trailblazer, or Escalade w/V-8 will snare you one that should be factory stamped for 145 Amps. The AD 244's are *underrated* and often a unit sold even stamped for 130 Amp service will still offer up 140 easily. Going the junkyard route will get you the alternator for $25 or so, and then all you will need to do is find a slightly larger serpentine belt. (By about one inch) Doing your big three upgrade with this beast in place with 2 ga. battery cables picked up new and off the shelf will more than compliment this upgrade and your audio setup as proposed.
The AD244 can be rebuilt in a garage in an afternoon with a handful of parts off E-bay to make a whalloping 170+ amps with heavier GM issue rectifiers, regulator and stator coil swap. Rebuilds with double wrapped rotor coils and further upgrades will generate upwards of 300+ amps in the same large body alternator case and still be tough as nails reliable as the original factory built Delcotron/Adelphi unit.
The real rub will be if your alternator harness will be plug-in compatible. If you had some sort of late model CS130D "crossover" make of an alternator in there with a rounded, 4-wire harness plug, the AD244 replacement will be a drop in upgrade. Given the year of vintage on your car, I would almost be sure to say that this is an 85% bet in your favor. The larger case on the alt can be happily mounted with just the two bracket holes on front. The smaller case units had a third hole to bolt them up on the rear of the case that is still present on the large case swap out - but too large to fit the original bracket. Do not worry - the two front ones will be more than solid enough to work reliably.
About the only other concern is to see of there will be other harnesses, mechanical bits and hoses that may be in the way. The bolt holes are 6.5" center to center which makes them fit about nearly all GM applications and some Dodge without a problem. But the AD244 is thicker and deeper in it's build by a fair amount and you need to double check the fit before you permanently bolt it all together.
At worse, pick one up at any automotive parts place with a bullet proof return/refund policy and check it out - then hit the junkyard to find your generator gem. :D The physically larger diameter on the case will push it out from the bracket a little more than the stock CS/AD series alternator, needing the trial and error with several belts to get it done right. Generally though, the stock belt for your year/make +1 inch will more than suffice and be safe.
I am doing this upgrade myself soon to a '95 4.3 liter Vortec Blazer once I source my AD244 from a scrap yard and pick up the GM "Heavy Duty" rebuild kit. (For solid 200 amps at idle) :D Be mindful that there were two different types of harnesses that were used on these alternators depending on the year that they were produced. Some have just two blades in a socket for the harness, plus the +BATT post on the rear. THIS ONE WILL NOT and CANNOT BE MADE TO WORK IN OUR APPLICATION. If either your car or the alt you pick up has a square plug in harness adapter with 4 conductors, one of them being fatter than the other; a simple harness conversion can be done with a pigtail replacement available over the counter at nearly all parts shops.
Good Luck!(tm)
Life is too short to build slow computers or weak audio!