Unless you look at a hairdryer (turbo) or supercharger, then you'll have to loose some streetablity, and gain a four -speed auto to win at the drags.
It is impossible to gear a car with a 3-speed auto for 13"s and still have it streetable for an open road cruise. If it's manual, it'll never win a bracket race, some wheelspin, and it's all over.
That being the case, the 250 would have to produce power at 5500 to 6000 rpm, and rev to 6100 to 6600 rpm, to give enough power at the rear wheels. You'd need a minimum of 305 hp at the flywheel to get 240 rwhp, and about 280 hp at the flywhel for 210 hp at the bags. Maximum torque would come in at 4100 rpm to 4800 rpm, about where maximum power is now. Going to triple carbs allows the excellent intkae properites of the alloy head six to be pulse tuned.
Chrylser points the way that Ford boys have to follow. Triple carbs, or a big 600 cfm 4-bbl. A 650 Holley or double pumper is fine on a smaller Cortina, but it sucks gas on the street. If you used a Barry Grant 500 2-bbl #2300 Holley with a 1.75" throttle kit, removed the choke horn, and flycut the main venturis out another 62.5 thou, and made up a Dominator -style stub stack for each venturi, then 290 hp is possible, for almost 230 rwhp. The Ultraflow intake would work well with this.
None of this could be done unless you ran a later model EF/EL crank relieved to clear the cam and drive the distributor, or at least some AU rods of 6.06" and ACL Race pistons. There is a need to match the kind of spec Chrysler used for there 265 E38/49 engines.
Generally, people have unrealistic ideas about how a six can be made to scream. If you are loosing 40% of the capacity of a 351, or 20% capacity on a 302, you have to make it rev the way most V8's don't, and gear it perfectly. Commodore THM 700's and demon diff ratios of 4.1:1 are the go here, a 2.77:1 diff with a BW 40 just won't cut it.
You can't create power without extra revs, and a loss of low-end torque, unless you turbo or supercharge. An engine is just a big pump. See how the lastest 182 kw Falcon has to run to 6000 rpm, and produce power at 4750 rpm, 1500 rpm up in peak rpm, and 750 rpm higher than the old EFI 250, despite a vastly more efficient head and engine management system.
