Well, I've spent some time trying to determine a good location for this check valve. I really want to keep it behind the firewall, but there's no good place for it. The most likely option is between the two spar brackets, but it's just a little bit too long. After thinking about this some more, I decided that maybe I'll just make a new body for the check valve that has an AN-4 port on one end. That will eliminate the reducer and save me about 5/8 in length. So, I took the valve I bought from ACS apart and took a bunch of measurements. Then I did some redesign using the dimensions for an AN-4 fitting from MS33656 and came up with this drawing. My friend, Shane, said he could make this part for me, but that's before I knew how complex it was. I'll see if he still want's to do it.