"30% [to be paid]upon X's acknowledgement of receipt at the factory, the balance upon receipt at C's plant".
This looks like I am trying to get round tackling your question head on, which I am! Justification? I think the fact that X has to "prononcer" his receiving [the goods] is important and that if you turn your sentence around this way, then "acknowledgement of receipt" just runs off the tongue so easily... Adding where they are delivered means the problem is avoided.
Maybe those who know more may know whether "acknowledgement of factory receipt" is said or not. It does not sound natural.
réceptionner = receive, take delivery of, check and sign for
As for "acceptance of works" which is used in the construction industry, I would be a little reticent about using it here.
Larousse Business Dictionary (FR-EN-FR)
Robert & Collins