(a) Force and effect 
Subject to the provisions of this chapter and to any valid intervening rights acquired under laws of the United States, any mining claim located under the mining laws of the United States subsequent to July 31, 1939, and prior to January 1, 1953, on lands of the United States which were, at the time of such location

shall be effective to the same extent as if such mining claim had been located on lands which were at the time of such location subject to location under the mining laws of the United States: Provided, however, That in order to obtain the benefits of this chapter, the owner of any such mining claim shall, not later than one hundred and twenty days after August 12, 1953, post on such claim in the manner required for posting notice of location of mining claims and file for record in the office where the notice or certificate of location of such claim is of record an amended notice of location of such claim, stating that such notice is filed pursuant to the provisions of this chapter and for the purpose of obtaining the benefits thereof.

(b) Labor and improvement 
Labor performed or improvements made upon or for the benefit of such mining claims after the original location thereof shall be recognized as applicable thereto for all purposes to the same extent as labor performed and improvements made upon or for the benefit of mining claims which are not affected by this chapter.

(c) Withdrawal or reservation 
Any withdrawal or reservation made after the original location of such mining claim affecting land covered by such mining claim is modified and amended so that the effect thereof upon such mining claim shall be the same as if such mining claim had been located upon lands of the United States, which, subsequent to July 31, 1939, and prior to the date of such withdrawal, were subject to location under the mining laws of the United States.