340 Pistons with 10.5 CR with X Heads???

That is what I am aiming for. Hope port and flow the X heads up to around 250 cfm at 500 lift. I think I can do it with mild pocket porting gasket match and the 2.08 intake vale with 5/16 stem diameter. Then top it with a gasket matched air gap intake. Stock steel crank with lighter rods and pistons. Hope to get up to 450 HP with a torque curve as broad as possible. If that means higher comp ratio and maybe rough street manors I am ok with that. Not like I even have the time to drive it every day. I want the car to scream like a bat out of hell but still look as stock as possible.

Thanks for all the info. I think I need to get my heads done first. Then CC them before deciding on milling either head or block. But if I come across a good enough deal on a KB 243 or similar piston I might pull the trigger and make them work.
My OOTB edelbrocks flowed 255@ .550 Im running an XE282S w/ 10.8:1 compression. 428 HP @ 5800. Im thinking you may fall shy of 450 HP. 400 sounds more likely w your combo unless you go more compression, more cam or get them heads to flow a little better. JMO