The article I referenced said that the uneven distribution could be made up in the following year even though that would be an uneven distribution.
"The regs do include a helpful example, however:
S, a corporation, has two equal shareholders, A and B. Under S’s bylaws. A and B are entitled to equal distributions. S distributes $50,000 to A in the current year, but does not distribute $50,000 to B until one year later. The circumstances indicate that the difference in timing did not occur by reason of a binding agreement relating to distribution or liquidation proceeds.Under paragraph (l)(2)(i) of this section, the difference in timing of the distributions to A and B does not cause S to be treated as having more than one class of stock"
I wouldn't create a loan document, I would just do a catch up distribution in the following year, nothing more should be needed