Maybe look at one for an 88 F150 5.0. I know they have a check valve similar to the one I had on my 78. Mine rusted out, but since the pump wasn't hooked up right anyways and in the way for my P/S I took it all off. You may have to adapt it some how, but it will at least get you back to working legally again.
I can tell you that the F150's uses a 3/4" pipe thread to screw to the air manifold. Don't remember the top side though. It is located at the rear of the engine above the bellhousing, there is a manifold that goes into the rear of each head. Maybe even a trip to the JY can find you one?