please help me identify which v8 vortec I have

This question has been bothering me since im owned the truck.I have a 1965 chevy stepside truck with a 2004 Marina engine in it.I know its a vortec and from a boat but that's all I know.are they any SURE way I can tell if its a 5.3 , 5.7 , 6.0 and what horsepower its rated at? Are they like a bar code sticker I can scan like im seen on other newer Chevy motors.I checked the pad in the front of the engine on the pass side and its blank.does anyone know of any other numbers or other ways of telling which motor I have? It has a TH-350 trans bolted up to it and a edlerbrock performer rpm intake and Holley carb.

 

Most of them I have seen have a manufacturer label on the valve cover but the serial number and engine size are also on the back of the block above the flywheel cover. Probably is a 5.0 or 5.7. could be a 6.0 but i doubt a 5.3.

 

will I had to remove the transmission to find the id numbers

 

The displacement will be in the casting on the left rear side of the block, behind the head.