Another 273 question

Any cam that you install, and I mean any, that has a later-closing installed intake angle, will lose cylinder pressure as measured by the compression test.
The loss of cylinder pressure shows up in the engine as a loss of bottom-end torque/power.
The 4bbl does not cover this, because
A) it rarely opens below the stall speed and
B) even if it did, at up to say 2800rpm, the engine is well fed by the 2bbl.

The ONLY way to get the low-rpm torque back, in a given engine is to:
1) up the cylinder pressure back to at least what you had with the previous cam. OR;
2) with chassis weight reduction. Towing is the opposite of weight reduction. OR;
3) with a higher stall convertor, but this mostly only helps in first gear. OR
4) with Torque multiplication. But this only helps at lower speeds. Whereas;
5) increased cylinder pressure works at ALL rpms and ALL speeds.
6) supercharging, lol.
IMO:
What you need is a 340, with a 273/318 sized cam, and small-port heads, and an appropriate build. That'll give you at least 25% more bottom-end torque and power, even with just the 2bbl. I have already done this, in 1974ish, and can tell you, that it was a dynomite street runner in a 65 Valiant wagon. With a 4bbl you get the added passing power.
The increased bottom-end torque would allow you run less rear gear, equivalent to about the percentage difference in the Engine sizes. That means you can run about TWO sizes less rear gear than you now have. Say from 3.23s to 2.76s. This will reduce your hiway rpm by the percentage difference between the gears, which equates to better fuel economy. Will it meet or exceed the 273? that's a tough call. In steady state cruising, I think it would.
But it will be so much fun getting up to speed and hammer-down passing, that who can say, lol.

OR
as others have said;
just freshen the 273 that you got, and drive it.