Just a heads up.
You said that you have a manual trans.
Probably this trans has a 3.09 low.
But it's a 2bbl engine which could have a rear gear of 3.55 or probably less.
Let's say it is in fact a 3.55..
Your starter gear is thus 3.09 x 3.55= 10.97
If your engine will idle like stock 2bbl cam, say 550rpm in gear, then your slowest roadspeed is 3.66 mph. with 24.5" tires.
But if you have say 2.94 gears, and a later 2.66 low-gear trans, then 550 will be 5.13mph
But if your engine will not idle smoothly below 700 in gear, then 6.53 mph.
The point is this;
Do you need to drive this car slowly?
If the answer is yes, then, you need to know;
what rear gear is in it, and
what low-gear is in the trans, and
what your tire roll-out is,
and then, you need to know how slowly your engine is willing to idle at. This will depend an awful lot on the cam, the compression ratio, and the ignition timing. If you have to retard the ignition timing like I do, to 5*, then the entire bottom end will be weak.
That's quite a lot to have to think about.
BTW-1
for your application, I find no fault with your factory 273 2bbl cam, assuming that it is serviceable.
However, your engine can easily be converted to run a hydraulic lifter, and then you can run a stock 318 cam, or even, a stock 360 2bbl cam.
When it comes to bottom-end power, pumping up the pressure is already gonna give you more power. ANY cam with a later-closing intake event, is automatically gonna drop some pressure, which will drop the low-rpm power, and likely need to idle faster. and if it idles faster, it will drive faster at idle.
BTW-2
Somebody has got to say this, and if I'm the bad guy then so be it.
If you are looking for more low-rpm power, with a 273, then your best bet is more rear gear. Going to a 3.55 from a 2.94 is a 21% increase in torque-multiplication, which will make each gear feel that much more powerful. The downside, of course , is the higher cruising rpm.
Alternatively, a 318 is plus 16.5% a bigger engine, and will do the same thing without the higher cruise rpm. And the deal with that is, all things being equal, even a stock smog 318 will out torque your hopped-up 273. Put a 4bbl on the 318, with your closed chamber heads, with a free-flow exhaust, and your 64 will be a whole new animal, with only a modest loss of fuel economy, which you can easily get back with less rear gear.
There, I said it