4 bbl intake 273

There is your problem
27.5 mph with 24" tall tires and a 2.73 rearend is about 2700 in first gear.
But
it is 1600 in second, or perhaps stall speed if a 1750 TC is in there. Well at that low an rpm,that poor 273 ain't got much.And a 4bbl will not help it one tiny bit at these rpms.
Next 47.5 mph is 2800 in second, but
it is 1920 in to third, and now the 273 is bucking the wind, and so deviding it's power between that and the chassis.

So there is a very simple solution to this, and that is to get the transmission to stay in each gear a little longer until you find a satisfactory rate of acceleration, that is doable by the stocker. edit; by the stock engine.

Here is what you need to do;
A) Go make sure your 2bbl carb is opening all the way when someone else floors it inside from the drivers seat! As in, the floor mat is not in the way,lol, or the throttle cable is misadjusted, or something else is preventing the throttles from opening ALL the way.
B) Go figure out what your rearend gear ratio is. I have been assuming it is a 2.73 or 2.76 or a 2.7something,lol. If you need help, see below.
C) but if it is not a 2.7 something then STOP!, do not continue! Report back and I will have to recalculate the speeds. If you have a tachometer, then you can do continue but do not exceed 3800rpm. I do not know if your old 273 can take more than 3800.
E) if it is a 273 rearend;Then go for a drive, and hold it in first gear until 38mph before you manually upshift into second. This will be about 3800 rpm. When it shifts into second it will be at about 2250rpm. Let it climb up out of that hole, and hold in second until 65 mph,then upshift it into Drive. 65 will be 3800 again.
Now if that rate of acceleration is fast enough for you, then we will have to adjust the tranny to make it happen by itself.

)To figure out the rearend ratio;Plan A
1)Block the front wheels so the car cannot roll, even the tiniest bit.
2)put the car in neutral
3)release the park brake.
4)Then, jack up one rear wheel, and block up the car so you can safely reach the rear end. Do not shimmy underneath the car without a safety block of some kind near to the rear wheel opening,but under the frame.Be safe;block up the car!
Ok, now grab the tire and rotate it. If it turns then grab a sharpie, and shimmy under there. If it doesn't turn you have a SureGrip go to plan-B
5)Turn the pinion yoke so it is pointing out somewhere towards the jack,where you can see it from out there. Put an index mark on the yoke with the sharpie and another mark adjacent to it on the rearend. Ok now crawl outta there, and go over to the hanging-down wheel. Have a peek at the marks you made,can you see them, and are they still lined up? If not,make them so.
6)Now, grab a chunk of 2x4 or or a similarly sized cardboard box, or anything that can span the distance between the bottom of the tire and the ground under it.Lay it flat beside the tire.Make a sharpy mark on the tire at the bottom most point, and a mark adjacent to it on whatever item you laid down there. One more time check the marks under the car.
7)Ok, what you are gonna do now is turn the tire exactly one revolution, while simultaneously counting the number of turns that the yoke on the rearend makes. Be precise! You will get a number between 5 and maybe 7. Go!
If you get lost turn the tire backwards to the beginning point and start over.
8) Finally, divide the number by two to get the rearend ratio. You should get a number close to one of these;2.7,2.9,3.2 or perhaps 3.5. So if you didn't get one of these, Do it over.
9) be safe;block up the car!

Plan B
1) you will have to get both wheels in the air. And
2)do not divide by 2 in step 8 above.The number of turns will be the rearend ratio. Be precise.There is very little difference between some of the gear ratios; less than 1/3 of a turn in most cases. If you give me erroneous numbers, and your engine blows up, that is on you. You may have to shimmy back under there, to find the difference between 2.7 say and 2.9 ratios
3) be safe! block up the car!