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

I appreciate everyone's help thus far, thanks for working with a complete newbie.

I am struggling to understand the compression situation. All the information I can find on these pistons are flat top, at most a 4cc dish. If I was to use a steel shim at .028, assuming a deck height of .069, 70cc for heads, and 4cc for the pistons, I am getting 8:1. Taking into consideration altitude as mentioned it will be even less.

With flat pistons, and .020 shims (as claimed with Fel-Pro 375-SFL8553SP) I am getting 8.44:1 before taking altitude into consideration.

I am just looking to get ~230hp out of this to match what I suspect the 273 had on a good day. And again, I'll be using a edelbrock performer intake and 4bbl carb to help out with that. Headers as well if they'll fit.

Am i getting closer on this, or still way off?

-edit-

If I continued with .020 or even .028 gaskets, would I be in a good enough spot to just run it and swap some low cc heads on it later?