Now I have another question.  It may be that I just haven't looked in the right places for the information I want, but I can't fathom what's going on with the pickup in the second photo.  The reason I made the part on the left of photo 1 was to provide clearance for the four disks that are staked into those recesses.  What are they there for?  There are four galleys leading from the inside of the center hole to the four recesses.  They look rather like freeze plugs, but the physics looks wrong for protecting against overpressure.  If I use the spacer on the right, do I induce some risk by blocking those disks?