I have a pair of Tunnel Port heads ( C7OE-K casting ) that I had flow tested at R & R Performance in Spring Lake Park, Mn., the same place Jay uses. They have not been ported and use stock size valves ( 2.250 intake, 1.750 exhaust ). They are aftermarket valves, I'll have to look up the brand, but nothing too fancy. Also just a fairly standard valve job, nothing trick. Here are my flow figures:
Intake:
Lift .100 .200 .300 .400 .500 .600 .700 .800
CFM 60 124 205 242 280 305 323 325
Exhaust:
Lift .100 .200 .300 .400 .500 .600 .700 .800
CFM 58 108 144 176 185 190 191 192
The intake ports, although generous, are not actually tennis ball size. And like most stock Ford heads of the era, the exhaust ports are the real limiting factor - they are basically the same as any generic FE, but with the larger size valve. I can't answer your other questions, I know some of the engine builders on here have experience building Tunnel Ports, hopefully they chime in, along with maybe Joe C. I believe someone on the forum had posted info on their Tunnel Port build in the past.
They did well for what they were designed for - NASCAR and LeMans - the wins prove that, but like lots of this vintage FE stuff, there are better modern aftermarket options now when you factor in the cost.
