"...on an m14..." You do know that's not a bolt action? In any case, you'd be converting from a rimless case to a rimmed case that is less "powerful". You'd have feeding and magazine issues. And you'd need a completely custom barrel as the 7.62 x 54 uses .311" bullets.
"...just about impossible..." Anything is possible with enough time and money. In this case, it'd be lots of money.