I recently bought a used vortec engine to swap it into another truck, but i don't know if its a 4.8 or a 5.3.Is there any way to tell with out opening the engine.Also I dont' know what it came out of cause I heard you can find out by the vin #.

 

I've read that the easiest way is to pull a plug and shine a light into the cylinder at TDC. The 4.8 has flat top pistons and the 5.3 ones are dished.

 

I believe the 8th digit in the vin will tell if it is a T or z it is a 5.3 if a v is 4.8 if u it is the 6.0
hope this helps.
Dave