Check out this picture of my 69 Camaro L78 VIN stamp, near the oil filter. Pretty fricken hard to see a number there. Press and hold down the mouse key on the picture in the link below and you can see where the numbers were. It's the original born-with block, no doubt about it now, but would've been near impossible to verify without close-up digital photos and Photoshop.
VIN pic:
L78 interactive block stamp