225 /6 at 250HP?

I can't argue with what's been said, but I'd like to throw in another option.

To travel 80 mph for hours atta time and realize good fuel economy, and hit 14's is not rocket science. But the roads to get both are a bit at odds withe eachother.
The tricks for the former are relatively simple; light weight, low rpm, and small engine.
The tricks for the latter are just as simple; a favorable power to weight ratio.
The turbo is a very effective tool to make both happen.
If your pockets are deep and you have lots of time, then the turbo route will certainly get you there.
But your goals do not necessarily REQUIRE a turbo slanty
But in NA (normally aspirated) mode 14s are easy with 275 hp, and certainly possible with a tad less. So that means almost any 360 will get you there, even a LowCompression 2bbl 360 has the potential. It however will need some help. And a 3 speed automatic is not gonna do it.
To cruise at 80, comfortably requires an rpm of under 3000. To get favorable fuel mileage, the Rs will need to get down to 2000 or thereabouts.
So here are the final drive ratios(FD) to hit all the bases NA.
Quarter mile; With a junkyard 360 hoping to hit 90 at mid 14s you are gonna need to trap optimally at something like 5200, so 4.56FD will do it. You will want at least 3 gears to get you there.
80 mph cruise; to hit 2000 will require a 1.92FD ratio.
There are no current appropriate 4-speed autos that can turn a 4.68 into a 1.92, as this requires a .42 o/d ratio.So a compromise will be required. A .69 is available.
So now we need to bias things a bit.
No 1, the junkyard LC360 is out. You are gonna need more power to pull a lower gear to 90 mph and you are gonna need more efficiency to up the mpgs at a higher cruise rpm.
So what kindof ratios might be more appropriate?
Well with a .69 o/d, lets bias for mpgs and choose 2200 for a cruise rpm, and 27 inch tall tires(255/60-15). This will be 3.23s. So then it remains to build enough power to hit 90 with 3.23s. With a 360 as a base this is pretty easy. You just need the usual mods such as headers, a 4bbl and reasonably high compression. The stock 360 cam will maybe get you there. A 220ish fast-rate is almost guaranteed to break 100mph, and I built one that hit 106 with 3.55s and a 4speed.That's a PW of 10.8, so at Dart weight of 3350 say(car and driver), that is 310hp.(Did I mention it was easy?). (106 is actually in the twelves)

So there is your NA recipe; small high efficiency engine(360) with an O/D auto and 3.23 gears, plus light weight(3350)

It should be said that mid-14s could just as easily be achieved with a teener. Hitting 14.5 requires a pw of just .060. At 3350 pounds, this is 200 hp. The teener however is gonna need optimum gearing. It's not gonna do it with 3.23s. So you will have to bias the teener for the ET, and then your 80 mph targets will be compromised. Well the teener could do it, with a stroker kit.

So now what remains is cost and uniqueness, and time.
As to cost;
So sure the turbo slant can do it without the O/D. But the stock 7.25 is not gonna last long putting up with all that torque. So the slanty needs a rebuild with a hi-flo head, plus a complete rear and beefed up tranny, plus the turbo kit.
The NA kit is a Hi-Compression unported 360, with an O/D auto and the stock 7.25 will last a long time with nothing more than a good-working SG.
As to uniqueness,
yes the turbo slanty fits the bill.
As to time
Since you will be doing all the engineering on the Turbo kit, Things take time. A lot of time. And one day the thought will enter your mind;"sheit if I would put a V-8 in this thing, I coulda been driving it 2 summers ago"

See the V8/904 route is quick and easy, and the combo can be fine-tuned as you go.Even with 2.76s out back, the V8 will motor along nicely doing a reasonable job in stock form.That gives you time to find and build a suitable O/D tranny, and then your car will only be down a week or two, as you fit it into your chassis. And as to the engine, again you can spend an entire winter building your powerhouse the way you want it, and drop it in in the spring, over a long weekend.Eventually you might decide that the gears are just too low, and so you gather up the parts, and when it's ready, it rolls in in a matter of hours.
With the turbo combo, It is more or less an all-or-nothing deal. If you don't upgrade the tranny and rear at the same time, it just breaks. And then there you sit, all sad-faced knowing the clock is ticking.

And don't forget the suspension, steering and brakes. With added power, comes added speed requiring the chassis to keep up. Again, with the turbo, you can get into an awful lot of trouble relatively quickly. The V8 is a little more relaxed outta the gate, and doesn't usually wake up until a later on down the road.

Obviously only you can make the final decision, so all the best to you, and may all your schooling end in A-Plusses.