my girlfriend just pulled apart her B20a, and i was talking to a friend of mine and he was saying to give it a bead hone while the pistons were out

so, i think its an 81mm bore, but i'm not sure where to get one, the only place i found has an 83mm bead attachment, but had like 6 different abrasives on them, i'm pretty lost here, anyone shed some light on this?

this is all i could find

GB and GBD from Brush Research Manufacturing

thanks