Sorry, you got the wrong one.
I did too, but the local Pick-a-Part where I pulled it off a Taurus 3.8 had a 30-day exchange, and I was able to swap it for the right 7" spacing 3G that came on later 3.0 Taurii. You need a 7" bolt hole unit.
As far as I could research, all the "big case" 3G's were 130a, while the small case units were either 90a or 110a. When I say "big case" I'm talking about overall alternator case diameter and not the mounting bolt spacing. I think all small case 90-110a 3G's were 7" spacing, while big case 130a 3G's came in both 7" and 8" bolt hole spacing (and you got the latter -- a big case 8" 130a unit).
You can find the small case 3G's on Windstars and Contours and they'll bolt up, but don't crank 130a. The only 5.0 Mustang difference between 7" big- and little-case units being that you need to shave a small chunk out of the alternator bracket on the 5.0 motor to make the big case 3G fit. A small case 90a unit will bolt in without modification but obviously, you want the big case 7" spacing 3G to get the full 130a. No worry though, because the bracket trimming job was simple with a dremel tool mounting a small cutting disc. You can see pics on a bunch of websites but don't sweat it -- it was simple. I didn't even mark it and eyeballed a good cut that only took 5 minutes.
In any event, the big case 130a units could be had with either 7" or 8" bolt hole spacing, and you got the wrong one. I also worried about the "clocking," meaning the angle of the dangle on where the wiring connectors face in relation to the mounting bracket, but I found it really doesn't matter. The car's wires will do just fine connecting to a common-as-weeds 3.0-Taurus-big-case-7"-bolt-hole-130a-3G, even though the wiring connections seemingly point the wrong way. Just make sure you don't have any short-circuit risks with the 3G's hot output post being in near proximity to the passenger side head. But mine cleared just fine.
Also, the most common Taurus 3.0 7" big case 130a 3G units, which are probably the most common units you can find anywhere, have an extra mounting point for a small bracket on the back side, which is a sizeable bump that looks like it might not clear the passenger side head on a 5.0. In fact, it clears just fine and the extra bump is no problem.
I am running a $20 big case 7" 130a 3G I pulled off a late '90's 3.0 Taurus motor, along with a PA performance 4-gauge charging wire. The extra wire is a must, but you could make it yourself for about $25, rather than the $50 PA performance charges. I did not change alternator pulleys at all and in the end, it was more simple than it sounds: The one Mustang alternator plug with a half-round side just plugs straight into the new 3G. The other rectangular plug gets the small white wire spliced to a 3G connector that plugs into the one lone hole on the 3G, and the two black-orange wires on the old rectangular Mustang plug are abandoned in place. These are replaced in the system by your new 4-gauge wire with a maxi-fuse in it that runs from the 3G's hot wire post to the car's solenoid battery post. End of story.
My $20 junkyard unit works like a champ with the dashboard gauge sitting at 14V no matter what load I throw at it. Don't freak out too much over this one, it turns out to be much simpler than it sounds.
