Just bore the 216 block 60 over (actually .0625") and use the 235 pistons "as is". You'll increase the displacement to 224 cubic inches, raise the compression slightly, and reduce the tendency for the Babbit rods to wear as rapidly due to the lighter piston weight. You'll also be able to turn a few more RPM without beating the rods to death. Unless you've got a cam-grinding machine, simply turning the pistons on a lathe won't work- - - -the piston skirts aren't round. Their widest point is at right angles to the wrist pin, and the piston gets round as it heats up because it has an Invar anti-expansion strut cast into the piston pin boss on both sides.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!