Mopar had longer tubes available also, made for top fuel cars. Call a Top Fuel team, they will help. Most are super nice people. Maybe glue the Mancini spacer to head and use one gasket?
I like the mechanical 6 Pack too, just built one for my 440. I think if you calculate the airflow test pressure difference, the 6 pack is around 960 CFM? Changing the center carb from 350 CFM to a 500 CFM would help. Maybe I need one for my hemi??? Does the 6 pack work good on a short runner intake?