383 Build - Help!

OK, dummy alert- this is a little confusing to me, but I know with a little help I can get this right, eventually.

Ring end gap- I really don't know how to address this.
My understanding is the 915 heads are 78.5 CC.
What the chambers on the heads are cut to? I was not aware that this was needed, or frankly what it is. Are we talking about cleaning up the chambers of the heads, or shaving the head surface?

About a year or so ago I bought open chambered heads and I was informed the compression would not be high enough and I should get closed chamber heads. I was going to use the stock 915 heads on the original engine, but I came across these 915s with the bigger exhaust valves supposedly the best you can get.

So where do I need to be with the compression?

I want to drive this thing, as much as I do now, which is alot, but without the tired engine in it now
I want to get it right, and avoid mistakes, but the reality is there is a cost concern, and no one I trust or know well enough around here.

Should I take this thing apart, or start over?
Someone say no, please.