:facepalm:
Chris,
the obs motor is based off the old SBC, with just a basic change in the intake, heads, and throttle body. they have decent low end torque, but are not powerfull by any means.
the 5.3 is based off the LS series motors, which is a completely different platform, and is a far more efficent motor.
Many people have made the switch between the 2, and generally the hardest part is the wiring. just because there is so much to do. and its not something you can half ass (dont want to be broken down chasing a loose wire)
to make the swap you can generally bolt any LS motor in, as they blocks are all similar, biggest differance is aluminum vs cast iron.
The 4.8, 5.3, and 6.0 externally look exactly the same, except for casting numbers ect.
just remember if you do the swap, you will need the adaptor for the flywheel IIRC, depending on what power adders you have or what motor you pick, your trans may not stand up to it. (the 6.0 generally will blow up a stock 4l60e becuase of the power. unless you baby the shit out of it), also motor mounts, exhaust, and a few other things.
Just some thoughts to help clearify some facts.
