Hi, i have a 77 425 motor and i need a rear main seal installed. my mechanic wants to know if he can get to it without removing the motor. he also wants to know if its a one piece or three piece???? he also wantsto know if he needs to drop the cam....these are all his questions...basically, how tough of a job is it and exactly what is the best way of doing it without removing the block. thanks much.