Thats cheaper than my solution was. I had/have a Griffen radiator that I purchased for my 6-8 swap, but it had the early mustang passenger side. Instead of trouble shooting like you did, I just bought another Griffen radiator so I didn't have to mess with it. If I had only known.
So on that note, does anyone want a brand new Griffen radiator for an early mustang? Never been run, only mocked up! Ill even include a Gates 23308 Hose.
1966 Coupe, V8 Swap to 306 with Heads/Cam, AOD, 8" rear with Trac-Lock and 3.42 gears, full Hotchkis/Global West suspension, Wilwood 6-piston 14" brakes up front, Wilwood 4-piston 14" brakes in the rear, oh! And Air Conditioning.