There are several problems with building a tunnel port. One is that you have to use a stock intake, there are no aftermarket intakes. Second problem is most of the heads you find are cracked or have had impact damage in the combustion chamber. Its tough to find enough good pieces to make a tunnel port. Finally, a high riser is easier to assemble and makes as much or more power, so why bother with a tunnel port?
You can buy brand new Blue Thunder tunnel port heads that flow real close to what a SOHC flows, and flow more than a tunnel port.
1912 Model T Ford touring Salmon (ugh!)
1913 Model T Ford Touring original Black paint
1915 Model T Ford Roadster Black
1915 Model T Ford touring Black of course!
1967 Cougar GT 390 Cardinal Red / Black
1968 Cougar GTE 427 Augusta Green / Saddle
http://www.supermotors.net/vehicles/registry/15029/50071-2