what solid cam is equivalent to a hyd 268 ?

In the early As, traction is gonna be your biggest enemy.
So much so that I would run all the 273 stuff you got back there, the lack of HOOK will protect them...... at least for a while
Everything bolts right up AFAIK.
If you run a 318/340 short stroke crank, get the lightweight hypers which weigh about the same as your 273 pistons. If you're going with a sane street cam, which is all the lightweight-A needs, then you might even run the 273 crank and early rods, or the 318 stuff, to make internal balancing easy. You already have the later rods, assuming they pass muster, so a 318 crank in a 340 might be pretty close. The hypers might be a few grams heavier,(than the 273s), but not much.
Factory 273 pistons are listed at 549 gms, 318s were 592, 340s were 719 forged items, so don't use the 340 pistons/crank. The rods are all listed at 726gs, and in 69,they were all bushed.
BTW 360 hypers are ~502, so don't think 273s have the market cornered on fast reving.Mine is lightning.
So to recap; the logical choice is hypers, late rods and a 318 crank.... into either the 318 or a 340. Lotsa guys have bored 318s out to 340specs. This is also a logical thing to do in a lightweight-A running 3.55s with a small cam. If you do this with a 340 you have to change your thinking from all 340s were screamers, to Oh, Gee this 340 makes torque!....... cuz you're only gonna need a 262ishFTH cam . You can still buzz it up to whatever, with the right springs. And with the torque of a small-cam 340, you can run log-manifolds and even should you desire, closed chamber 318 heads or better is Magnum heads.
As I said elsewhere, I have run this exact combo in a 65 V100 Wagon and it had zero-traction, so the heads were not the limiting factor, although I did run headers.That was one of my most fun combos ever; and it was just thrown together with junk I had laying around.

Now as to balancing, I don't understand the problem; You just bring your stuff to the machine shop and let them work it out. They will weigh it all out, and tell you your options. You supply the Front damper and the flywheel and they take care of it. Or in the case of the 318 crank into the 340 with say KB107s, it's gonna be real close already.In fact, there is a chance your current crank and rods might be pretty close with those KB107s into a bored out 318/340.I say this cuz all these many years later, that 273 crank is an unknown.
Maybe the thing to do is take your 273 crank and a couple of rods over to the machine shop and have them calculate what weight piston will work as-is, and knowing the weight of the hypers, they can tell you, what will have to be done to make 'em work.Then you can make a decision at that time.
Or just weigh your current 273 pistons, and compare them to the hypers. At least you'll get a picture,of where you need to be.

If you went with a 360, there's all kinds of pistons made for those, and many of them are close to stock weight, and many have extra material on top that you can mill off to set your Q, perfectly. The icing on this is you can run an even smaller cam,and fry the tires at will up to maybe 50/60mph in that Lightweight-A. Or you can swap to 3.23/2.94s and lose a bit on the bottom,(of which with 355s, you are gonna have way too much anyway), and gain some hiway comfort and mpgs.
But like 66fs says you're gonna need a bigger clutch.....sooner or later.
And balancing that second flywheel is no big deal if you have the specs of the first one or just bring them both to the shop.