Upgrading my XPS 8500's Video Card and PSU, have Encountered a Problem

Hi, this is my first post on the support forums, and I have a couple questions.

So I have been doing some research and I would like to put a new video card and PSU into my XPS 8500. I am fairly certain that the EVGA GTX 970 SSC 4GB will work as a replacement to my current GT 640 1GB. However it would be nice to have a confirmation on that, though.

Now, onto the PSU.... I have acquired a lot of stress between finding a PSU that's compatible with the GFX card and that fits into the PC. Up until today, I thought I had a definite choice for a PSU. However, it turns out that I have just found one more factor that I have to consider. I think (key word: think) a Corsair CX750M will fit in there even though the case is microATX and the PSU is standard ATX. Today, I was looking at the owners manual, and I discovered that there are two clip-like things behind the standard 5.5" PSU that are supposed to hold it in. The CX750M is about 6.3", or about 160mm. My question is will the CX750M fit in the XPS 8500, or will I have to find a PSU that is the same size as the stock PSU?

Any feedback/help is greatly appreciated!