I quite seriously doubt the frame is 501. More likely 531 with the 3 worn out of the decal. Your frame is a Carlton, made in 1972 (that's what the G is for). The Competition was one of the top bikes in the Raleigh line-up. Below the Profesisonal and International. You can compare the components to what's listed in the specifications here -
http://www.retroraleighs.com/catalog...talog-1972.pdf to see what's original, and what's not. Don't take the specs as complete gospel though. Raleigh is well known for their bikes being a bit different from what got printed in the catalog.
Nice find...