No costs related to project work can be charged after the official end date of the project.
Within the 60 day window, you can only charge costs that are related to producing the Project final reports. What this means is that you cannot produce the final reports until you have incurred all the costs. If the review falls within this period, then do NOT send "Final" reports before the review. Send only excellent drafts – but they have to be drafts. Once the review is over, submit the "Final" versions.
(Of course the exception to this rule is any Certificate on Financial Statement costs that you may have.)