There really isn't an established set deck height on any of these engines, but typically on the 250's it has been found to be as much as .050"-.060" below the deck to as little as .020" below the deck. Depending on how many times the engine has been rebuilt in the past and if the block has been resurfaced a few times before you ended up with it. Your measurement of almost a 1/4" of an inch makes me suspect you have a 230 and some one installed 250 pistons into it. That would explain the excessive deck height you have. See if you can find a part # somewhere on the piston somewhere to verify someone didn't make this mistake.
