340 wall thickness & deck height

you want to bore to the least amount as possible to get straight cylinders....as far as decking...that is about normal for a small block mopar...left to right and front to back different...If you want a perfectly square block then deck it.....you need to figure out where YOU want for a deck height....your pistons..rods and crank...

and unless the rods are blueprinted to 6.123 center to center and the crank throws are perfect at 3.306. and indexed....perfectly 180 degree opposite each other on the journal....your deck heights will vary even with the block squared... cause there is tolerates in the rods and crank...