If it's a Guardian Roy, what I would do is just bottom the thing all the way out to start with... probably 70 or 71. Then I'd make two turns ata time on each opposite limb bolt, making sure that you don't skip one... It's probably going to take at least 10-12 turns on each thread due to the close threads used on that model's limb bolts to get her down in the lower 60's. I suggest bottoming it out to start with so that you keep the tiller as close to even as you can while you're adjusting it down.

After you've loosened that limb bolt 6-8 times on each end, I'd try it... turn it down one more time, try it... turn it one more time, and try it. Keep doing that until you're comfortable with the draw weight. Like Matt said, if you used to shoot 60 regularly, you're not going to take that down too far before finding a comfortable draw weight for you.