since you have a loader needing dual valves one sa and one da, and you have a selectrol valve and a single da valve available.. you got 2 options.
use the selectrol diverter valve to run a hyd line out to a dual valve, and then plumb the return of that dual valve back to the sump with a fitting into the dipstick plate... lift the 3pt handle to start the oil flowing to your open center loader valve. this valve won't see 3pt lift loads as it will be isolated by the diverter, so a cheap-o 120$ log splitter valve that is oc and has one da and one sa configurable port will work.. just pull the knob on the selectrol to cut hyds from the 3pt and send them to the laoder.. and vs-vs.
or.. use your da single valve as a feed for a dual valve setup that is pb capable, as it could see 3pt loads.
lastly.. you could get a sandwich palte that goes under that single valve you have.. use that valve for a remote and then plumb in a power beyond valve off the ports on the sandwich plate.. thsoe plates go for about 100$.. plus whatever the laoder valve is.. probably 120-150$
lastly.. you could just keep looking for a dual ford valve to fit the top cover... used ones int he 300-500$ range.. new in the 700-800$ range.
soundguy