273

The Baby Commando is a fine motorvator for that Lightweight A.
Any other SBM will be a fine replacement. All can be made to work with your A833.
I have a Commando trans behind my HO360, with a 8.75 at the back, and they are all doing very well.

The only cons I see with a bigger engine in the early Barracuda, for street-duty, are;
1) the lack of rear wheelwell room to accept enough tire for to make a bigger engine worth it.
2) money
You should be able to fix that 273 and slam it back together fairly cheap. But if considering simultaneously a rebore, well then the money is, IMO, better spent on doing the same, on a bigger engine, cuz it's gonna cost the same, maybe even less.
An early hi-compression 318, will get you the same power, but as a 2bbl. Whereas the Smog-era 318, with your 4bbl on it will be torquierr but similar power to your 273.
Any 2-bbl-318, is gonna tax the small tire tires fitted at the back
And any bigger engine is pretty much overkill to the tires.

Performance makes heat and pretty soon the cooling system starts to complain.
As power goes up, your exhaust manifolds are gonna be the choke.
Pretty soon, one thing has led to another and the darn project has become a money pit.

What would I do?
Well,
I got this 340 block in the corner, and
a stack of heads including a nice set of closed-chamber 273 heads, and
a 360 2bbl cam, and
a few years ago I found an Offy Dualport which still has not found a home, and
recently, in shed #3, I found a box of TQs that I hadn't seen in 22 years, and
I know I have a set of 340 Exhaust manifolds hiding somewhere, plus
I got one A833 overdrive left in the basement, and somewhere,
is every rearend from 2.76s to 3.55s , all with posi's, yes guys, I said posi's..
But, I guess I'll need a bigger clutch, wohoo, got that too!
Surely;
I could put some thing together.
Where do you want it delivered? lol. .

Oh BTW
I could bring you a 273 core block; I mean it's on the way an'all....