I see this is an older post but thought I'd chime in. I have built two 360 engines with the same set up as you are using. Same Speed Pro pistons, flex plate and xe268h cam. I weighed both set of original pistons and then the Speed Pro's. All of them were within a couple of grams of each other. When I talked to my machine shop he told me for a street car the factory balance job is fine. The H116CP pistons are OEM weight replacement pistons. I'm sure the factory balance job wasn't meant to be spun up to 7000 rpm's all day but one of my engines has done 6500 many times with no problems :) You will love the way it runs. Just did another one with same setup but with a Lunati Voodoo 10200703 cam. The Lunati has a little better street manners. If you are running an automatic you will need a torque converter with a 2400 stall or it will be a turd off the line with either these cams though.
