Guys I had a very nasty 273 in my 64 Dart, owner the car since 73 and it has gone from stock to a factory type 235 HP 273 to a D dart spec and eventually ended up at a 275 HP to the rear wheel which factored out to about 340 at the crank. I ran low 13's with a 4.10 and a 727. Had to spin it 8k to make that kind of power. The 273 will loose torque fast as posted early in this thread if you go long on cam duartion.
The key is fairly high compression, lots of initial spark timing and a high lift short duration, low overlap cam. Even if it is a street 230-250 hp at the crank engine. Sire a 318, 360 make more HP T etc. But if you want to keep the 273 get a custom set of pistons in the 10 range and cam like 480-515 lift max for street. 625 Carter, or Holley is enough omn a modiified 2 plane to act like a torquer, decent headers and a 2 or 2 1/2" ex is plenty. Do a bowl cleanup job on the heads, port match the intake, do a great 3 or 4 angle valve job, back cut the valves etc. , if you have the money replace the guides and go taller valves with smaller stems spring seats etc. If you go oversize valves shrouding is an issue. I have the origional Mopar bible from 78-79 and I am telling you high 13's even on todays crappy fuel is obtainable in a street car that is not to wild.
You can get it into the low 13, high 12s in an A body but then it is more a race/bracket car. You can do at a decent price a 230-260 HP engine, only gotcha is the custom pistons. I think I priced a set of Ross pistons for like $600 a set. When you go custom you are gonna do forged since:
#1 you need to spin the think 6500-7500 anyway to make peak power
#2 the cast custom are about the same price when you do custom sets.
I used a forged 318-3 truck crank back in thr day, windage tray modifed steel rods etc but a 340 unit crank if you can find one would be a plus, and also you have to outway the money to rebuild the rods, high strenght bolts etc or just get a set of Eagles, Do a good balance job (A MUST)
Anyway you can make it run. I did and I even ran circle track at the old Ontario 500 speedway.. Dam I am old huh!
I now run a 416 with over 500 HP now in the Dart and the Torque and throttle responce is amazing! No substitution for inches...
Wish they had a 360 or a stroker back in the day. Largest option was a 340 or a 318.. 360s were $$$ and had just come out when I was building the car 1st go around.
Good luck have fun, and determine how much MONEY you want to spend, this is the real key... Hell I know a gus tht ran 10s in a 65 Valiant with a 273. PS He was spinning that 273 9k and no it was not a street car, neither was mine, even though I did take it out at times...
lso did not mention above but if you want it quick you need 3.91 + gears a loose convertor at 3k stall or more, and or a 4sped with a 10 1/2 or 11" clutch. Dont waste time on the little 9 1/2 " clutch. You will fry them up. I did 18 times in 3 years.