Another Set Back (very Frustrated)

HERES AN UPDATE, PULLED INTAKE, CAM AND PUSHRODS LOOKED GOOD, OUT OF COURIOSITY I PULLED ONE HEAD, EVERYTHING LOOKED REALLY GOOD, UNTIL I APPLIED PRESSURE TO THE NUMBER EIGHT PISTON. THE THING MOVED 3/16 OF AN INCH. IS IT SUPPOSED TO MOVE THAT MUCH? THE OTHERS DONT MOVE AT ALL. COULD POSSIBLY BE A BEARING OR WRIST PIN I THINK THIS IS WHERE THE NOISE IS COMING FROM. I WILL PULL THE PAN LATER TO CHECK THE BEARING. MY QUESTION IS IF THE BEARING IS GOOD CAN I JUST CHANGE THE WRIST PIN? or should i do a complete rebuild. this is an original low mile motor THAT IS VERY CLEAN. THE CYLINDER WALLS HAVE NO RIDGE AND THEY ARE SMOOTH AS YOU CAN GET. MAY NOT NEED MACHINING. BUT IM WORRIED THAT LACK OF OIL MAY HAVE CAUSED THE PROBLEM. CAN SOMEONE PLEASE POINT ME IN THE RIGHT DIRECTION. I DONT MIND DOING THE WORK. BUT I ONLY WANT TO DO ONE TIME.
THANKS