I can help in part. The birth date is from a Family Bible first printed in Holloways of the South by C. J. Stevens. I know this record is reliable as as I descend from William's sister, Elizabeth. The birth date given for her matches that given in a different Bible owned by one of Elizabeth's descendants (it also is consistent with census records). I believe their are other transcripts of the first Bible online.
I do not know the source of the death date. However, years ago I found a record related to the record of William's estate in Jasper County. I do not have a copy or transcription but it was dated 10 March 1826. I suspect you can find it online on Family Search, probably in Book 7. Unfortunately that book isn't indexed.
If you find it I'd appreciate you sending me the Book and Page number so I can relocate it. Also, any other information you may have on William and his two wives. Thanks.