I've changed the topic!!
Glass blasting is a bad idea. The glass pieces will remain in the pistons and will come out when the engine and oil gets hot. This can cause serious damage to either your pistons, block, bearing, etc.
I've ended up with buying new pistons. Don't want to risk having the engine rebuilt and do it all over again.
Better is to soak them with mr muscle or any furnace cleaner and let them in for a min or 15 and then use your wifes toothbrush

to clean the pistons. (You might also use an old toothbrush to avoid an angry wife / girlfriend

) Or buy her a new one, that's lot cheaper then having to order the pistons!

To clean the ring lands just break the ring that comes out and clean it with that.
So:
Don't, don't, really don't use glass media blast. They say blast with walnut shells shouldn't be a problem, but i don't have experience doing that.