318 build up

Well, I too, often jump on the more cubes is better.However, this time, Im having other thoughts.
Those early Barracudas are around 400 lbs or so lighter than the 2nd generations. That means the equivalent of pretty much 40 cubic inches.So a 318 is almost equal to a 360.
Then theres the tire fitment issue. Not much fits back there.Certainly not enough for a healthy 360.
Then theres availability. John doesnt live in America,home of plentiful iron.
And then theres the budget. Stuff from friends is mostly free.
And finally, John said "no parts are decided yet, but the 714 heads is going to be used." Thats a pretty definitive statement.
So it looks like this is how it may be;
The 714 heads,the free 318 block, and the free forged crank.Thats a pretty good start.

The very early 318s had the same early 273 rods, so if this is going to be a lo-performance teener, you can use your rods. If your gonna abuse it, then a switch to the later bushed rods would be better.Those late318 rods have the same casting numbers as the 340/360 rods. However the 360 rods are a press-fit pin.The floating-pin 340/318 rods allow you to assemble the pistons onto the rods yourself, and makes later piston mods easier.
Next is pistons and rings. This is the place to spend some money. Now,again,we come against the budget.If you see more performance in the future, I highly recommend a zero deck. This allows for a tight quench,closed chamber head design which will really wake that teener up.To that end, I recommend a piston,tall enough to be machined down to be fit the decks, and thus making a zero deck engine.If the 714s are an open chamber design, then I would buy quench-dome pistons and carefully fit those in there. They can be machined down at a later date,to zero-deck for a closed chamber hi-perf head, if the opportunity comes up. And in the meantime, you can reap the benefits of sorta tight-quench and hi-comp. I dont know what octane fuel is available out there, so this will have to be engineered by you.
Its hard to get a decent Dynamic compression ratio from the teener with its smaller bore,short stroke,flat-tops, and open chamber heads. Knowing this, the Static c/r and the camshaft need to be carefully co-ordinated. Those two are very nearly married.If you allow the Dcr to fall too low, the off-the-line performance will also fall, and you will forever have to rev it up and slip the clutch to get moving. That gets old in a hurry.So to that end,get the Static c/r up, Then you can manipulate the Dcr, with the intake closing point, so that you can use the available gas.
To illustrate this; Say,you can get the Scr up to 10.8,then to get the Dcr down to 8.5 for 93octane gas will require an intake closing point of 65*ATDC. Thats a pretty small cam. And requires a pretty small TOTAL chamber volume of 67.5cc,also pretty small.(thats about a 60cc head,an 8.5cc FellPro blue, and +.005deck flat-tops ). I told you it was hard.
Here is another combo;The 57cc chamber head and the .020 gasket.
However this combo does not suffer zero decks. The piston would need to be dropped about .015 down, to get .035 quench(piston to head clearance).This would get you 11.25 Scr, and with a 70*ATDC point would net 8.5 Dcr This is about a 1 size bigger cam.
For me, I would just bite the bullet, and buy a custom cam.

The point is this; if the 714 heads are open-chamber, I think you are really limiting your build options. Both combinations here illustrated are with the early closed-chamber oem iron heads.
EDIT;This from MoparTim; "714 heads are closed swirl port head with factory hardened seats." So it looks like you are good to go.

Having said all that,John, Many guys have been happy with a 268Comp cam in a low-compression teener. At your curb weight, you could be too.
Im wishing you every success
So now you have, or nearly have, a compete long-block.