YOU SAID:

He put his hand down into the empty space where the floorboard had been

INTO JAPANESE

彼は床板が置かれていた空きスペースに手を置いた

BACK INTO ENGLISH

He put his hand in the empty space where the floorboard was

INTO JAPANESE

彼は床板があった空きスペースに手を入れた

BACK INTO ENGLISH

He put his hand in the empty space where the floorboard was