Rod bearing tests. Back before catalytic converters, yea I'm that old
We would remove one plug wire at a time & listen at the bottom of the "V" near each con-rod location. The theory was if the noise deminished when the combustion pressure in that cylinder was absent due to no spark ... then you had a fair bet you had a con-rod bearing problem. A piece of broom handle laid against the block near the bottom would transmitt the noise fairly well to your ear. If the noise was higher up along the cylinder bore & you had to follow it up & down thru the stroke...you could guess it was a wrist pin, if the noise stayed low down you could guess it was a rod bearing, if the noise stayed fairly constant it was a main bearing. I don't know how well that method would work on an LT5, as crank is burried fairly well.
If no one else has any suggestions, I would offer this up for consideration: Gordon Killabrew has a website..."foryourcar.com" and he has a paid trouble shooting phone line...it might be worth the $ to hear his opinion & suggestions? JMHO.