Thread Chaser

I have a d16y7 block and need to get a thread chaser to clean the holes for the head bolts to go into.Does any one know what size chaser i would need and where i can maybe find one

I don’t know what size thread chaser you need but Sears sells thread chaser kits for pretty cheap. Just don’t snap the chaser off in the block! I’ve seen that done before and that makes things worse.