See my edit above ^^
I'm pretty sure you can screw your pressure sending unit (PSU) into the stock galley plug that's located right under your alternator. Check out THIS THREAD
, it's not car specific, and it is a Defi install, but I couldn't see the install for your gauge being much different. The only problem that you might run into is if the PSU doesn't fit in the stock galley plug. It looks like it's the same thread size, so you should be okay.