340 compression ratio

i have a ‘71 340 I bought a couple of years ago. Was told it was a “fresh”build. I pulled the valve covers and the oil pan, it was nice and clean inside so I put it in my car and ran it a bit. It always kind of annoyed me because I couldnt get it just right. I messed with timing, carb etc and still wasn’t real happy. I recently pulled the trans to overhaul it and decided I’d go a little further on investigating the engine. I figured I’d pull it apart and ck the bearings and was interested in the cam that was in it and if it had been installed correctly. The guy I bought it from was not positive or convincing on what cam was in it. The bearings all look real nice, unfortunately no sense in going any further with the cam as it has a lobe thats probably about to wipe out. Nice little divit on the bottom of the lifter. Anyway what I’m getting at is I’m gonna replace the cam, degree it correctly and put er back together. What I’m interested in doing is finding out the compression ratio. The pistons are still in the block, so if I know the bore and stroke and I cc my heads and decide which head gasket I’m gonna use is there an accurate way to determine compression ratio with an unknown piston manufacturer to get the specs from it.