Original Engine? How can I tell?

[XSoph]

Hi. Is there a definitive way to tell if my 5.3 vortec is original to the chassis, like a matching VIN stamp? I bought an 07 Suburban LTZ a couple weeks ago and been fixing it up. It has 150-170 psi compression on all cylinders which seems a little too good for a vehicle with 251,*** miles. My concern is that although the top end seems in good shape I have no clue how old the bottom end on this motor is. Any tips?