1970 340 has the 1973 low compression pistons

For a streeter
and 3.55s
and a 2.66 low gear A833;
Your starter gear is only 3.55 x 2.66 =9.44.... so if you cam that 8/1 engine up, the CCP will all but disappear turning her into LESS powerful than 318 up to about 3000/3500.
Furthermore, with a 5500 shift rpm, you won't get into Second with those 27" tires until 47 mph, but 3500 is 30 mph, which if the tires won't spin, is a stinking long time. Then at 47mph, the Rs in Second will start out at ~4000, going to 5100 @60 mph.

What I'm saying is that
IMO
For a streeter, with 3.55s, a 340 cannot afford to have a soft bottom end. You will cry about it every time you take it out.
How you get the pressure is up to you. There are just two ways; 1) decrease the Total chamber volume or 2) close the intake valve early.

Here's what I mean;
Take the 8/1 340 with the factory 268/114 cam. in at 4* advanced, the Ica will be 64* and the Wallace predicts just 119psi CCP, at a very modest V/P of just 94.
That V/P number is barely bigger than a 225 slanty (87), and not even as strong as a smoggerteen (114 in Maine @600ft)
So even the stocker was already soft down low. With No hi-stall, you are married to that stinking V/P of just 94.
For big fun, you will want that V/P to be up around 170, but you can't do that with Iron heads, nor with a 3.315 stroke.
With iron heads and a stock stroke; next best is maybe 130/135 V/P, but that will require a careful co-ordination of parts. This would make your very low rpm to be very powerful, for a 340, which is always a joy.

But if yur the kindof guy who never runs down low, or who doesn't mind reving it up and slipping out the clutch, well then just put me on ignore. But before you do just remember that 30 mph in Second gear is just 2550 rpm, but in First is 3530, so I guarantee you that as a streeter with 3.55s, you are sorta married to low-rpm. Think about that as you are choosing a cam.
BTW; you should chose the cam first and then build the engine around it. To do otherwise is just inviting disappointment.
To machine the heads, you also have to machine the intake and sometimes the china walls as well, and then you need custom-length pushrods too. Imo the better solution is just to swap out the low-compression pistons.
But if you decide to run a tiny cam, maybe you already have enough CCP. For instance, running the factory 318LA cam will get you an Ica of 48* and the Wallace predicts..... a V/P of 121. Oh well, better than 114, I guess...........