I agree. There's a header above that small bay to the right, and I can't penetrate through it for obvious reasons. What I can do... is exactly what you're saying -- moving the combo fitting into the right bay, and then venting up and eventually 45 the vent back in to the bay above the washer box. Thanks for the good points. I'll post a picture when I'm done.
That wall isn't CMU, it's a product call rock lath. It was used, around here, during the 50's. It's a 1/2" gypsum board with holes in it, came in 16" widths. It was ran perpendicular, and then it was covered with 3/4" of concrete. Plaster was textured on top of that for the finished product. It's the in-between from lath and plaster to drywall.