The 383 is a low block, 440 is a raised block. You can tell by looking in the area where the dist sits. If there is a raised pad directly opposite the dist, it is a 440. You can also check the side of the block, it will be cast into the side of the block showing year and size.
Most 440's will have "440" stamped into that raised pad on the front of the engine. You may have to scrape paint off to see it. If it has "440HP" you have a winner. The attached photo shows a raised block (440) you can see the pad on the one in the photo is marked with some type of black markings.