“Then they arrived at the house of Reusre, and found him standing with his kilt upside down.”
I suggest that this is because Reusre is a constellation that has travelled through the sky in a circular motion, we are therefore seeing Reusre including his kilt upside down. Given the number of characters in the Westcar stories that I have identified to constellations, I had marked a possible connection between Reusre and “The Standing Man” of table 6.2 in Lull and Belmonte. The only real reasons there being that The Standing Man is standing and wears a kilt.
There is another intriguing possibility, which is that of Sah (refer Table 6.1 of Lull and Belmonte). On p181, Lull and Belmonte referring to the Zodiac of Dendara tell us “Sah is easily identifiable as the man holding a was sceptre as a personification of Osiris, and Sopdet (Sothis) is represented as a recumbant cow on a bark with a five-pointed star within her horns which is obviously Sirius. The cow, a symbol of Hathor, suggests the assimilation of Hathor with Isis and hence with Sopdet herself”
Hathor is an alternative name for Heqet, one of the musician gods of the story. So could the Reusre be associated with Sah and therefore Osiris? According to Joshua Mark of ancient.eu, “The name `Osiris' is the Latinized form of the Egyptian Usir which is interpreted as 'powerful' or 'mighty'.” So could we be dealing with Re-Usre where Usre is another form of Usir, the Egyptian name of Osiris? This would weight my bias towards Sah being the correct interpretation of Reusre.
 Nederhof, Westcar Papyrus accessed from [mjn.host.cs.st-andrews.ac.uk] pp 122 - 207
 Lull and Belmonte, The Constellations of Ancient Egypt, accessed from [www.iac.es]
 Mark, Joshua, Osiris, accessed from [www.ancient.eu]