Mounting alpine bindings

If anybody could help me out with this, I would appreciate it. I have an old
pair of downhill skis that I picked up recently that seemed pretty good, and
were the right size for me, but they had old bindings on them. I was thinking
that they would make a great second pair of skis for spring skiing or for use
on days when conditions are less than optimal. Anyway, I bought a pair of
Solomon 637 bindings on eBay, and I want to install them myself, but since I
have never done it before, I need a few tips. My plan is to put them on myself
and then take the skis in for a tune-up and binding adjustment. I understand
that you have to find the ski balance point with a straightedge, and I do have
the right mounting screws, as they came with the bindings, and I know that you
have to fill the screw holes with epoxy glue. What I don't know is where
exactly do I position the bindings for mounting? How do I know how far apart
to put the bindings? Do I just hold the bindings up against the boot, or what?
And do I balance the ski with the boot in place? Any tips would be greatly
appreciated
Thanks