The main goal of getting the piston up closer to the deck surface is to try to obtain a better quench clearance. A distance of .040" to .060" between the head and piston is considered ideal, it not only helps you gain a slight bit of compression, especially if the pistons are far down in the cylinders as a 292 is, but helps obtain a better burning of gas by really squeezing the air/fuel mixture into a tighter space and helps reduce the tendency of detonation if you were to have too much quench.
Checking the piston deck is more involved than just taking a wild guess at how much to cut the block surface, it requires you to physically insert each piston and rod assembly into their respective cylinders and not only make a measurement of how far down in the cylinder it falls, but you have to check the pistons at the side where the spark plug is as well as the quench side, never at the center of the cylinder. You will then rock the piston from side to side and measure how far up and how far down each side of the piston moves, and from this you can calculate the deck height of that side of the piston, and how to compensate. You need to simulate exactly how the engine will be run as far as making sure all the machine work is completed, such as crank reground, rods reconditioned, cylinders finish honed, block rough decked, etc....Trying to do this before the machine work is completed will introduce error to your readings at every step and compound the inaccuracy of your measurements significantly. You will find that often, to obtain your desired deck height, not only will the block need to be final decked by some amount, but most if not all of the pistons will need to be cut on one or either side as well to equalize them for zero or whatever you determine to be your objective.
It does require some specialized tools like a dial indicator with a stand to span across the deck surface, and this would also be a good time to degree your cam, so a degree wheel would also be a good investment if you don't already have one in your tool box.
