I posted this also on Chevelle Tech 2001.
A friend just had his 454 rebuilt,,after two days spent we got her reinstalled with no problems. The engine builder and the BOOKS say to break the engine in at 3000rpm for 15 minutes,,,so we did 2 5 minute sections at 3K each. The engine started sorta hard (like the timing was not right,,couple of carb. back firers) then engines starts hard,and the headers just glowed big time red and hot. This occured on both 5 minute runs. At the end of the second 5 minutes we had developed a minor rear oil leak and coolant leak. My question is should it be hard to start ther engine and should those headers glow like that(HOT). Are we big time off on the timing ,,maybe to retarded/advanced and how do we correct if your suppose to run engine at 3K,,,how do you set the timing??????? Could the water leak be from the new freeze plugs setting up???? We have one more 5 minute section.Thanks for any input.

I have always ran them at 2000 rpm for 15 minutes without stopping. The timing should be set closer first. Sounds like your timing is retarded. One way to set initially is to remove #1 plug and wire, turn engine to 8 degs before TDC #1 cylinder, turn ingition on, slowly rotate distributor until plug fires. You can do this a couple of times and it will get you close.
The coolany leak should be repaired before restarting. You can barrow a pressure tester from Auto Zone and pressurize the system to locate the leak.

Tom