Tom,

Often times the case to pulley dimensions on a replacement alt are not the exactly same dimensions as the factory alt thus throwing off the pulley centering. To combat this I often machine off some of the mount ear and then use shims to move it fore or aft depending which way it is off. If you google alternator shims you can sometimes buy them pre-made but they are often copper which i don't tend to like next to the aluminum or just use a piece of flat granite and some wet sand paper and shave aluminum washers to the right dimension. You want a snug fit between the mount ears so you don't fracture the mount by over stressing it and bending the ears in. Many of these brackets are cast steel, aluminum or iron and snap rather than bend so go for a good tight fit with your shims.

I have installed many alts on engines with similar belt wrap to yours and not had an issue once the pulleys were lined up. You can hold a ruler flat to the machined face of the alt pulley then use calipers to measure the distance to the belt at the alternator end. Then move the calipers to the pump end of the belt and see what the difference is.

As Rich said you could also have nasty pulleys that can create a lot of belt dust too.