Here's a link to a quick photo I drew up.
https://imgur.com/a/LMnDEpl
I only have about 1" of clearance between the bottom of the threads on the valve and the floor of the skimmer box.
If you're interested I'll elaborate on what I'm doing here. The box currently has a typical float fill valve (like a swamp cooler) installed in the "water supply" port. That works just fine when connected to city water because it just sits there and drips into the pool 24/7. I'm switching to a rainwater fill system that's lower than my pool, so it's driven off a very small pump. When I hooked it up, it wasn't pretty as the low flow rate of the float valve didn't sync well with the pump. Even with the addition of a pressure tank I ended up with the pump cycling on and off all day long.
The problem here is the float switch flows great when the level is very low, but the flow rate slows dramatically as the fill level comes up to the desired position. That's probably why they don't use float valves in toilets. Anyway, I searched for a valve that flowed much faster and snapped off when reaching a predesignated point and thought a toilet valve would be perfect (albeit it's nearly impossible to find specs on the flow rate of a toilet valve). That way I'll flow like crazy, and run the pump at full blast right to the point that I'm full, and then I'll stop the flow completely. Just like a toilet!
Another thought here would be a side entry toilet valve like
this but I've never seen one of these locally and I have no clue as to how fast these things flow and if they "snap" off like a typical bottom entry toilet valve.