Should I leave it Stock?

Yes and no.
It's not exactly a waste; it's just that;
the stock cam/carb/intake is good to say 3000rpm, so the 4bbl is not gonna do much until the 2bbl gives up..
and because of the small factory cam, headers are not a big help either. Taken together, you will get a power increase, but not until later in the rpm band. With a stall of say,1700 rpm, neither of those is gonna make a difference at zero mph when you hammer the throttle. With say 2.76 rear gears and those 15s, you might be looking at final drive gearing of 65=2200. If that is true then 2500 in first gear, where the power is just starting, will be over 20 mph. So from zero to 20ish mph, that 4bbl and headers is not gonna help you one tiny bit.
That 273 cam might power peak at 4000ish rpm, and the 1-2 shift might be 4400 so your power band is gonna be from no lower than 2500, to perhaps as high as 4400. So if you want rapid-transit to happen, you need to be in that band. The 4bbl, might not be fullopen until closer to 3000, and if you open it too soon or too fast, you will likely just bog down. Lets say you somehow make it happen at 2800. So then your 4bbl power begins at ~2800, peaks around 4000, and is rapidly falling off at 4400tops.
In first gear this is beginning at~24mph, peaks at 34mph and is falling away at 41 mph, The question is; does that help you?
In second gear, the power plateau might be at ~ 3600 to 4200. With 2.76s this is about 52 to 72 mph. Hey nice passing gear. But check out the hole from somewhere around 36 mph to 52 mph, where your engine is gonna be struggling.Even with the 4bbl, cuz she is off the cam.
But think about this;
How much power can you expect with the 4bbl and headers? and where is it gonna come in at?
I'll guess no more than 20hp at 4000rpm, more likely is 12 to 15
I'll guess zero at zero mph with a 1700 stall
I'll guess the power is linear from 2800 to 4000, so 1.67hp per 100rpm. It won't be linear tho, with less real power generated at 2800 than at 4000, but I just want you to see the point.
So;
if you are looking for more power to take off with from a dead-stop, then the 4bbl/header combo is a bust.
But if you want passing power from 52 to 72, it's hard to say no, to ~18hp
So

Yes and no.
Not as powerful as your combination but my 273 accelerates to 85 or so with authority. My 318-2 preforms about the same.