Another 273 question

Even better yet than a 318, IMHO. Especially with a low compression late '72 or '73 340 with your 273 heads. But in staying with a 273, here is what the stock cam is supposed to be
273 Camshaft Specifications

1965 ................ 273/180 HP '2-Barrel'

Type ..................... 'Mechanical'

Lift ......................... .395" Intake ~ .405" Exhaust {NHRA ... .400" ~ .411"}
Duration ................... 240* Intake ~ 240* Exhaust
Overlap .................... 16*

Intake Opens BTC ...... 14*
Intake Closes ABC ...... 40*

Exhaust Opens BBC .... 52*
Exhaust Closes ATC ..... 2*

Lash {Intake} ........... .013"
lash {Exhaust} .......... .021"

Valve Spring {Valve Closed} ... #53 lbs. @ 1.69"
Valve Spring {Valve Open} .... #143 lbs. @ 1.31"
I'm not sure what lift they are using for advertised duration, but it's probably going to be impossible to find a cam with more area under the curve without a later intake closing event. The Oregon equivalent of the same cam on their site closes the intake 5 degrees later measured from .020 of tappet rise, and the two on the top of list before that one have much lower duration numbers, about the same lift, and close the intake at 35 degrees of tappet rise. It's not what most people like to hear, but a smaller cam to boost low rpm cylinder pressure isn't unreasonable in this instance.
Mechanical Camshaft Specifications