Safe? I would go no lighter than 8 grains per pound. I usually shoot between 9 and 12 grains per pound.
It sounds as though you have an older Grizzly with the B50 string. These are great bows! You will find that the heavier-weighted arrow will pack some authority should you decide to hunt, as well as helping to keep your bow quiet.
Most folks like to have an arrow about an inch longer than the back of the bow when at full draw. So, if you are drawing an honest 28", then 29" would be your goal. But if your arrows demand a little more length, then no big deal, go with what the spine of the arrow and the bow demand.
As you progress and develop your back muscles and drawing style, your draw may lengthen, so a little extra length in the arrow is a good thing. Stick with it, and happy shooting! (Oh, and I think the 500s are right as well. Clay and George gave you good advice.)
Killdeer