I know where you can get photos of U-129, ask Luc Braeuer he makes books about the U-boat bases of France and other books on U-boats, I saw a good photo of U-515 here that when I asked where it came from I was told from one of his books. I don't have any of his books at the moment personally but I've seen glimpses of them and they contain many of those rare late war photos of U-boats that you wouldn't find on the internet. So email him because if anyone has photos of U-129 from 1944 its him.
His email: grand-blockhaus@wanadoo.fr
Do it you won't regret it.
Btw, there's alot of surgery to do to the kit anyway if you want to make it accurate as possible, there's a lot especially if you want to do a different boat i.e: different hand bar placement on the conning tower different arrangement of drain holes... I can list them all, maybe you don't care for all that but I've researched the IXC's more than most people in that regard even for this forum and if you want me to go through all of it then I will. The IXC's are quite underrated.
Oh, do get back to me if you get anything.