Mike, If it moved that far then the catch for the push button is released and now it is just the "J" spring holding it on. Some are on there very tight. Make sure the gun is re-cocked. The reason for the Curtis Forend was because on the Field Grade a lot of these guns were losing the forend because of improper (not re-cocking) disassembly, causing the "J" spring to loose tension and the forend falling off in the field. This was started around 1913 and was discontinued around 1919. All guns with ejectors had a type of release built into the forend because of the added "kick" of the ejector springs. Also all guns from Ideal Grade up without ejectors had either the banjo style or the rectangular style roller release forend.
I would venture to say again that if the forend came down 3/8" it is just the "J" spring holding it on.