Is there a ridge at the top of cylinders? If not, I wouldn't be afraid to run new pistons without boring the block, just give it a light hone and go. I did my 360 this way. I prefer SpeedPro/TRW H116CP pistons over the KB's.
At spec they're about 0.016 in the hole and give about 9.25 compression with stock heads. I had my heads decked about 0.020 to get 69cc chambers and about 9.66 compression.

If there is a big ridge though, I would go ahead and bore the motor.