Sounds like a fun deal. Regarding tunnel port vs high riser, if you are sticking with the stock 427 stroke you will be cubic inch limited, so I would stay with the high riser. As a street engine you won't be winding it to the moon on a regular basis and the high riser ports are going to give you a lot more midrange than the tunnel port setup will. Why are you sticking with the stock stroke, by the way? If you could crank up the cubes with a 4.25" or 4.375" stroke crankshaft, either head combination would be streetable and it would be a lot easier to get to 700 HP.
Assuming you have your reasons for staying with the stock stroke, another reason to stay with the high riser is the dual plane intakes. That would be a strong street combination. There are dual planes available for the tunnel port but they are harder to find than the single plane tunnel wedge style.
I think you could put together a stock stroke combination that would run on pump gas and make 600 HP with the high riser heads and intake, a good roller cam, and compression around 11:1. The 427 sideoiler dyno mule I did for my book was like that. To get to 700 you would need a more radical cam, lots of headwork, and more compression, and you may not be able to get the engine to run on pump gas. But you could certainly get to 700 HP.
Just for interest, here's an overview of the combination I ran in my Mach 1 in 2005 at Drag Week; the engine was 511" and made 706 HP at 6300 RPM on the dyno. It ran no problem on pump gas, although I did use race gas at the track for safety margin reasons. I put about 2500 miles on it going to and from Drag Week, and during the event:
Shelby aluminum block, 4.375" bore
Scat 4.25" stroke crank
Crower billet rods, BBC, 6.700" center to center, BBC pin
Diamond pistons, 11.5:1
Comp roller cam, Xtreme Energy street roller lobes, 266/272 @ .050", .701/.711 lift, 110 LSA
Crower solid roller lifters
Smith Bros. pushrods
Edelbrock medium riser heads, ported to flow 335@.700" lift on the intake
Edelbrock Victor intake
Dominator 1150 carb
Hooker adjustable race headers, modified to improve ground clearance
I also ran a C4 with a 5000 stall converter, and a 4.11 Detroit locker rear end. The car ran 10.60s all week at Drag Week 2005. When I got back I hung a vacuum pump on the engine and ran 10.45 at a local track.
Good luck on the project - Jay