Is it allowed to re-format a post-print version of a published paper?
Since you obtained the permission for the journal to use a post-print version of the paper, you should be allowed to do that.

Technically, you have two options (depending also on the thesis requirements of your department/university):


add PDF pages to your thesis (which will look inconsistent with the rest of the thesis - and you are not interested in this option)
reprint using the thesis style


In the latter case, you might do the following to the page with your Chapter title (I would also make the chapter title = Paper title, but I don't think it's mandatory):

Chapter N

Chapter Title

@2000 Publisher. Reprinted with permission (Mar 15, 2003), from J. Doe, Paper Title, Journal Title, January 2000. DOI: XX.XXXX.XXX

Page break, followed by the reprint of the journal paper with thesis formatting. 

Notice, it is explicitly stated who holds the copyright (Publisher or Journal) and that this chapter is a reprint with a permission obtained at a certain date (you might want to hold either to the email from the publisher or screenshot with the permissions).

That is exactly how I added my already published papers (2 IEEE conferences and 1 IEEE journal) to my thesis according to IEEE permission.