Swapping '69 273 with '84 318 Into My 1969 Dart

No, for 318s, the stock gaskets were usually steel shim, .020.
The .069 number would be the deck clearance, which is how far below the decks your pistons are.
.069 is about 13.57cc, which has to be ADDED to the head volume.
OPEN chamber 318 heads usually come in around 70cc.
IDK; about heart-chambers, or Magnums, nor about the early 273/318 closed chamber heads, which seem to vary between 57 to 63cc, IIRC.
039 FelPros, which are actually 4.18inches round-bores, to fit the 4"Plus bores, come in at 8.8cc, and don't forget the Crevice volume of about 1cc.
This totals 70 +13.37 +8.8 +1=93.17, before you add for piston dish. This makes your SCR to be 7.99, BEFORE adding the dish, if any.
Some of those smogger-318 pistons have huge dishes.
And don't forget, Google says yur at 1300ft elevation. That's gunna cost you ~6psi CCP, (Cranking cylinder Pressure). Which is equal to about 3/10ths of a point of Scr.
So, even if your 318 was at 8/1 Scr, and was situated at sealevel;
by the time you get to 1300ft, it's making the same pressure as if the SCR had been reduced to 7.7/1@sealevel.
Pressure is heat, makes torque and times rpm, makes power. The less pressure you have, the less potential to make POWER.
This is not always a big deal, say for a grocery-getter. But, with a stock converter and short gears in the back, when you need POWER, it just will not be there, until the engine is running up on the shift indicator; and once you hit Second gear, it's all over.
These are all glitches that cam be overcome with gearing and stall, at added cost.
And
we don't even know if the coming 318, is still worth installing.