The drywall itself should not be expected to hold 60lb.
It's hard for me to believe that in 35" width, you can't find a stud.
I did find a page that may be helpful to you here
, but it seems to me that you need to start looking for a wall mounted bracket made for hanging heavy art. I've installed one before, they allow you to center the hanging hook anywhere between the studs. They look much like a mounting plate for a TV.
If you do decide to try to use a toggle bolt, use a back nut with a washer on the bolt before you spin the toggle nut on. This will keep the bolt solidly in place without falling flush to the wall. ALSO, do not overtighten the bolt! this will crush the drywall and lower the overall load bearing of the bolt. Drill carefully because punching a hole through usually knocks out a larger hole on the back, inside the wall. This makes a weak anchoring on the damaged drywall.