The maps below clearly show this pillbox to be in the location shown on google earth for S0004624. Mike Osborne’s book “Pillboxes of Britain and Ireland” shows a picture on page 148 which appears to be this pillbox but gives a grid ref which matches S0004824.
It is possible that it is indeed S0004624 which has since been removed as the date of the visit was  05/09/1973.
Google Earth View
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- PILLBOX (VARIANT): S0004624 7lmg pillbox.
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- PILLBOX: S0004624 7lmg pillbox.
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- PILLBOX: S0004624 7lmg pillbox.
