There's plenty of room under here on the frame, I'm looking at the tranny right now.
Honestly I'd put the filter in before it goes to the tranny cooler, the fluid will be at it's thinnest state when it's hottest and the filter should allow the fluid to pass quickly while trapping contaminants.
Idk how I feel about barbs for this, we are talking a lot of pressure here, maybe some stainless AN lines, I wouldn't mind even making new lines from the tranny all the way to the cooler to add the filter just for the piece of mind.