

If you want parallels the best source is probably the book _Temple
and Cosmos_ by Hugh Nibley.  It is not light reading however.

As to why these early practices "only parallel" and do not exactly
duplicate the modern LDS ceremony, there are a couple of reasons:

1.  Quite likely we do not have the exact original from ancient
times.  This stuff was not commonly known but bits and pieces
undoubtedly spread.  (Much as bits and pieces of the modern ceremony
get known.)  What we have in the 40 day literature, the Egyptian
ceremonies, and certain Native American ceremonies is almost
certainly not exactly what Jesus taught.