When they say light loads, what is meant is that it is best to stick to loads at the beginning end of the listings, not ultra light powder puff loads.
You want to use a powder that fills most of the case. Due to the large case volume, a very light powder charge can sometimes do wierd things, including detonation!
IT isn't common, and as far as I know, hasn't been able to be duplicated with regularity in testing labs, but it has happened many times over the last half century, with big magnum cases and light charges of powder, especially a light charge of a slow burning powder.
Stick to loads on the light end of what the .308 Norma is capable of and you should have no trouble from the ammo.
The rifle, on the other hand, depends entirely on who did the work, and how well. Have it fully checked out by a competent gunsmith before use.
Having just the chamber & headspace checked isn't good enough. Besides the question of how well the work was originally done, there is also the question of what ELSE a previous owner did to, or with it. They made it a magnum, did they perhaps shoot balls to the wall loads out of it? Enough to overstress things? erode the throat? etc...
Have it fully gone through, by someone who knows what to look for (and how to look) before considering it fully safe. Bubba is not the right guy to tell you this.
All else being equal (and it almost never is) bigger bullets tend to work better.