i would make absolultly sure that its rod knock before tearing that motor apart.
could it have been spark knock, or pinging. is he running premium fuel in this car.
about 90 percent of the time when I deal with rod knock it can be duplicated and then diagnosed.
yes i agree with the others that it may not happen at a load. but try this. True rod knock can be the piston hitting the head, or the side to side movement of the big side of the rod when the crank changed directions. if you remove the super charger belt does the noise come on instantly thats what mine did. the supercharger provides a sort of cushion in the cylinders that help keep the piston and rod in contact with the top of the rod. when you remove the supercharger it should get louder and be easier to duplicate.
have you checked oil pressure, fuel pressure and the basics.
when you do get the noise to be reproduced in a setting where you can get under hood and listen then you can start by carefully removing spark plug wires one by one (sounds strange but it works) the cylinder that is knocking will get very quiet. it works i have demondstrated this on a number of engines in the shop.
when I pulled down my engine and inspected it had number 2 cyl bearing was gone. it was almost welded into the rod and rotated 90 deg. i measured the crank and it had almost no damage other than light scratches and it measured good and was still round but the rod was fubared. I found a good short block to work with so I never fixed that motor so if you need a rod I have 5 great ones.
but before you condemn the motor you should have further diagnosis performed.