To remove an alternator on a v6 156, seriously consider getting rid of the car! Hours and hours of work.
Jack up & support on stands. Remove subframe, right hand drive shaft, serpentine belt. There's four bolts and two cables to go and out it comes... Think about doing the ARB bushes while you're there.
In fact, if you're doing the ARB bushes, think about doing the alternator brushes, especially if it's the original alternator and the cars done 140,000km or thereabouts. It's on borrowed time.
I'd never fit an alternator from a wreckers without checking the brushes. It's just too many hours to change it for just a few dollars.