I just picked up a 1980 f150 4x4 with a 400m(not original motor), it has a bad knock to it. i was planing on replacing the rod and main bearings. i'm pretty sure i can do it with out taking the motor out but i want to make sure. has anyone had any experience with this method? it's that or i might pull the engine and replace it with something different say a 4v 4.6L or a 2v supercharged 5.4L or a 3v 6.8L v10 or a 7.3L powerstroke. but that would take a lot of work with the drivetrain. let me know thanks.