On a '76 you have notches in the back for the rear cleats. Do you not want to use that area? They bolt through the transom. Putting cleats on top of the cap puts them in the way (I had 2 on top of mine for 20years) unless they recess. My 170 doesn't have the notches in the back (started in '72) so I put 2 popups in the back and one popup in front. You have the room under the cap but need to reinforce them so in case someone tries to lift the boat by them, they'll hold.If you want a midship cleat I think I would go popup. Google popup cleats and you can find them at surplus and discount places. I think I bought mine at Great Lakes Skipper.
I don't think you're over thinking it - you're thinking through it and that is what matters. Can you put a plastic hook on the line of the fender and run that line over the cap and hook into the cutout up forward for the rod racks? The cutout goes pretty far forward as seen in the pic below. And then you don't have to mount anything. Maybe hook the fenders fore and aft??