Could that be article in upended box for guest? (8)
I believe the answer is:
visitant
'guest?' is the definition.
(guest is a kind of visitant)
'could that be article in upended box' is the wordplay.
I cannot really see how this works, but
'be' could be 'sit' (sitting is a kind of being) and 'sit' is present in the answer.
'article' could be 'an' (indefinite article) and 'an' is present in the answer.
This explanation may well be incorrect...
'for' acts as a link.
Can you help me to learn more?
(Other definitions for visitant that I've seen before include "Shade" , "Apparition" .)