Can I use 3/8" toggle bolts to attach a deck ledger to hollow core concrete blocks?
Answers: not at all never, because for that application your cinder blocks entail to be filled next to concrete to have the tensile strength to hold the mass. If you can get access to the cinder blocks make the addition of concrete to them inside of the cells.
i say aloud i would be best not to-go ahead and run new blocks to support