BB cylinder head question

Well whoever rebuilt this motor used KB pistons back in 98 on the rebuild. Im hoping they put the right ones in it. If they didnt they will be coming out. I wanted to stay with the 915's to gain the bigger valve benefit and still keep the compression the same instead of going worse with the 906 head. I know the 517 heads are the closed chamber as well so thats the only direction I can go at the moment. I ending up finding a set of 915 magnum cylinder heads.