"Is fully transparent Delrin available?"
Not that I know of, but it can be dyed at injection time for other colors.
Be careful if you make yourself a custom housing Hal, we put ALOT of stress on it for good o-ring seal, since it's a big sucker, and the matting finish is not that good.
Your going to have to change the deep of the o-ring inset to reduce the stress and not risk cracking the poly housing. You may also have to sand the matting surface to get a good seal at the reduced pressure, or just try some sealant / grease
