So we have a 07 2500HD here with a 6.0 - should be an L69 far as I can tell. Weak oil pressure...knocked a bit. SO lets say it needs a full rebuild. New bearings, clean the heads up and rebuild them with some good springs a healthy street worth cam and then trying to throw it in my 2003 4wd Tahoe with a freshened 4L60e that's in it. Think its worth it? Too much of a headache? Someone told me the crank is different in the 6.0 and would have to be changed. Also said I may have to get a custom flywheel. I guess its my Gen3 Tahoe vs Gen 4 LS ? I'm still doing research so let me know what you guys think.
If you're gonna rebuild it, then the main Gen4-into-Gen3-platform problem isn't such a hurdle. That would be the difference in the reluctor wheels between the generations. The crank has to be removed to swap the wheels. It's an interference fit, so the correct way is to heat the wheel to expand it, then slip and/or tap it into position. It has to be clocked perfectly, so a jig is necessary. I'd bring it to a shop that has a jig and knows what's up. Make sure they use heat and not just cold press the wheel into place.
Aside from getting the correct reluctor on the crank, you'll have to extend wires for the knock sensors since they're on the lower skirts of the block instead of in the valley. You'll also have to extend the cam position sensor wires since the Gen4 has this sensor in the front cover. The camshaft position sensor is wired opposite between the generations, and you'll have to swap the two outer of the three wires on ("A" and "C" on the connector). Either unpin then from the connector in the harness or, if you're extending the harness, connect those two opposite of the other. I'd probably just use something like these conversion harnesses:
https://www.wiringspecialties.com/lsx-gen-iii-to-gen-iv-conversion-wiring-kit/ and move on.
The flexplate differences were for the earlier LS engines. I can never remember the specifics, but it's resolved by using the correct flexplate (dished or flat) and/or a relatively cheap spacer and bolt kit available from GM. I don't think you'll have to deal with this, but there's a chance since yours is an '03 and that '07 is mated to a 4L80E.
Here's some harness info to keep in your back pocket:
https://www.lsenginediy.com/sensors-inputs-guide/
