Joe ,
     "Back in the day" we tried to improve the dual port by cutting out the divider  from the flange inward by at least two inches. This did help ET but not as much as a "regular" dual plane. I have no idea what it might have done to fuel economy as these were drag race engines for bracket racing. On this tri power a cut back would remove the "last" turn down the air was being forced to do. As we all know every turn hurts flow.
    Randy

   All good . I only say that because I have been bit by the "exotic" part that didn't work before. More than once actually. The truth is EVERY engine part had an XE part number or SK ( which was normally for race parts) before it became an accepted production part and got a real part number like we are used to. Fan belts to fly wheels and everything in between.

   I am not a part of that facebook group but many consider me to be an Ford experimental part expert because of my 50 years of dedication to finding the stuff.
   Yes that is a Ford experimental part. It precedes the Offenhauser "Dual Port" by several years. Ford engineers did the design to explore better fuel economy until more power was needed. What they didn't realize initially was the tremendous increase is surface area and attendant "drag" that came along with it that seriously hurt overall air flow. While the tiny ports for the center carb did help fuel economy "some" , the "wide open" power was way off. IMHO , the manifold was likely tested by Ak Miller who was friends with Ollie Morris of Offenhauser  and the non patented concept was copied by them at a later date. Offenhauser did work with Ford over the years. It is important to remember not EVERY "experiment" works. This manifold is one of those. It WILL run and function.
     Randy

  Thank you I wanted to know before I cut up these NOS MR valves , to match the used XE valves. I'll probably put them up for sale.

   "Production" valves for the low riser / CJ were not hollow or sodium filled . The only 2.09x1.66 valves that were are the C8AX valves which were originally done as C6FE valves for the 427 LeMans engines with aluminum heads. They are fully polished and the intakes have a different shape , very noticeable. All of the valves were made by Eaton and have terrible tooling marks on the ID , further complicating their durability.
   Randy

   Do NOT run the OEM sodium filled exhaust valves for the exact reason you just experienced. They break!

   Ebay. but seriously look at the complete empty case OR one complete new one ready to go for $310.
    Randy

    Ross ,
        I buy the whole billet case and save the retrofit hassle ( truing and drilling /tapping the 1/4 screws). I have seen the "bell side" break too