I updated my OP with additional details in between our posts. Our approaches have diverged. The new information I have added strengthens in my view the reading that I have taken in that the Vth Dynasty Pharoahs are unimportant to the story line other than as possible diversion. The new information I’ve added does not confirm the year but does appear to encode some detail of the solar house. Unfortunately, the solar house is less than clear. Then we run into the problems of precession. I’ve included the details below of the connection of Osiris to the sun which are now included in the OP.
Nederhof, in his translation includes a footnote that to be historically accurate, Userref should be Userkaf and Keku should be Neferirkare. It is assumed that Sahure is correct as Sahure is the name of a Vth dynasty Pharoah. However, let's examine the evidence in Isis’ utterances that may indicate otherwise. Taking the first child, Isis utters 'May you not be powerful in her womb, in this name of yours of Userref!’ User is a name for Osiris as established above in the discussion on Reusre. Osiris is also connected to the concept of power and of re-birth. As such, I suggest that Userref is a re-birthing of Osiris.
Supporting this notion, Budge in discussing the Tuat on p179 “As the sun passed though the Tuat large numbers of souls made their way into his boat, and although it was only the dead sun that was their guide and protector, and his passage was through the realms of the dead which were under the sovereignty of Osiris, the god of the dead, they were brought forth at length to renewed life and light as soon as the boat passed out from the eastern end of the Tuat into the day.”. Budge further expands upon this by discussing the Tuat [pp 259-260] from the perspective of the cult of Osiris and identifies that there “lies a mummified form, representing Osiris, and called Sem-Ȧf, i.e., the “Image (or Form) of “Ȧf”” Further “As Ȧf, the dead body of Ra, passes into our world, his new life begins, and for men and women the night passes away, and a new day is born.” I argue therefore that Userref is in fact Osiris in the form of Ȧf and represents the rising sun in the morning.
Returning to the Westcar story, Isis utters 'May you not stay dark in her womb, in this name of yours of Keku!’ for the third child. Keku is the Egyptian god of darkness, which aligns to Isis invocation. According to Budge, “Kekui represents that period of the night which immediately precedes the day”. Budge further notes that Kekui was at one point considered an Elephantine god identified with Khnemu which came about due to considering Kekui a personification of the Nile god Hapi. Budge also informs us that at Kom Ombo, Sebek (a crocodile god) was a personification of Kekui.
The second child’s name of Sahure is considered to mean “He who is close to Re” with respect to the Pharoah Sahure. This combination of the third child Keku being the period of the night which immediately precedes the day, 2nd child Sahure being close to Re lends support to the notion that the first and therefore eldest child of Ruddjedet Userref is a form of Osiris-Ȧf and therefore represents the rising sun.