This is a request for only a head, of course the head needs to be attached to a body, so go with Kathar’s HEV suit body.
Now, to the head itself. If you’ve read the book Half Life 2: Raising the Bar, you know that it took a few people to create the Gordon Freeman head, however there was one person in particular of the Valve staff that influenced the look of Gordon the most, that person was Kelly Bailey.
Here’s the best reference I can find of him, it’s an interview way back from HL1.
I’d just say give him a slightly thicker goatee, glasses, and short cropped hair.
Please and thank you.