Okay brother, here's the low down from an 'analyse this' perspective. Please feel free to screw it up and use it as loo paper if you like....
The key is getting
a) the right power to weight ratio,
b) and then an axle ratio that allows the car to race through the traps at the end of the quarter mile at maximum revs for your engine combination.
Since you've ruled out 4.11:1 gears, this limits things a bit. I'll assume a 3.7:1 ratio from a Four-cylinder is the lowest ratio you want to use.
Example:
For a 2600 pound Cortina Six, you need a good 250 hp to do a 13.0 second quarter mile at 105 mph with you in the hot seat.
The maximum safe rpm for a 250 2v without massive modifiications to the sump, valve gear and internals is 5400 rpm, according to ex Ford engineers, and Kevin Bartlett (from Street Machine 1990, and 1995). This engine, because of its short rods and long stroke, hits a wall at about 4800 rpm.
The biggest wheels you can use and still tour the streets are 225/60 13's or similar. At 105 mph, that would need a 3.50:1 diff to haul trough the traps at near full revs. So as long as you've got a combo that gives 250 hp at 4900 rpm at the very least, and take it an another 500 rpm to 5400 rpm, then you'll do it.
Now how to get it!
Option One:-
I'd say to do this, you'd need to get a special grind cam from Wade, Crow, Speco Thomas, C.O.M.E, Kelford etc. You need to tell them what you wan't, and they'll tell you what combo of parts will be needed. If you want to use a stock intake manifold, you'll need a race preped 500 cfm 2-bbl with over siize throttle butterflies, and a fly cut venturi 62.5 thou bigger in both. Barry Grant sells them, and they are good for 290 hp.
Optionally, you could risk a very special cam grind that allows the 500 cfm carb to produce large scavanging ability, by limiting exhast flow at lifts above 350 thou or so. An example was given in a recent Hot Rod mag. But listen mate, your pushing a really fine envelope, and I've not seen it done on a six.
Whatever, you need a great cam, excellent exhast, top notch US/Aussie or similar valve sizes with inserts (1.76" intake, and whatever the biggest exhast valves you can find that fit in the head without taking out the water jacket or cracking the margin between each valve). Then you need a optimised ignition and better rod bolts and timing gears.
Its possible but this is expensive stuff, because to produce one hp per cube so low in the rev range takes a perfect camshaft.
You'd use a 3.5:1 diff ratio for this combo, or a 2.77:1 and take max revs in third at the quarter.
Option Two: Build the engine to rev to 5900 to 6000 rpm, spend on roller rockers, really good stock rods, or splash out on items like pened 3.3 Aussie 6.275"rods, or 6.06" AU rods, then knitt the up with ACL pistons. Hey, its only money. Then you'll need a Cortina spec High Energy Sump with a scraper and windage tray made up to control the torrent of oil at those revs. And look at going solid lifter or getting a real good hydraulic cam. Grab the cam, carb and exhast, and there an easy 250 hp at 5400 rpm hiding, no risk. Sorry buddy, you have to run 3.9 or 3.7:1 diff gears, and grab ear plugs for the cruise home. The other option, is going 2.92 or 2.77:1, and hold on to third at the end of the quarter.
Option Three: Nitrous oxide and a 500 Holley. Simple. Just use a 100 hp boost of funny gas, and build the engine to take it. Won't have to rev it past 4800 rpm, and you can use 3.23:1 gears and rev through the traps in top.
Back to your regular program...
