KB237's if you're getting the closed chambered heads. You'll want a domed piston if you're doing an open chamber head.

As for the bore thing, a machine shop can bore/hone a block for pretty cheap, then you don't have to worry about bore taper, ridge at the top of the cylinder catching the rings because you're running a different piston now, etc. Unless the motor has seen extremely low miles since the last bore job or you're going to reuse the pistons you have, I would bite the bullet and get it bored. You will not regret it.