DVW, to answer your question about pistons, I got them with the block. They were setup for the 4.375 crank. Talked to my machinist, and we discussed why the previous builder set it up that way. To help get the crank out of the oil better. He agreed, and said the 16ci difference wasn’t worth buying new pistons for.

mopars love fuel/air
Everything does

IMO you are going to be leaving some power on the table with the compression ratio for sure. Also depending on the cam it could be a make or break deal too. Lastly assuming the carb is a 2" throttle plate Dominator its going to cost you some power to. So I would say as listed 825ish +-25.

FWIW I did a very similar combo that was meant for our dragster but sold to a friend of a friend instead. Id estimate it makes 750ish. The only difference was it is a stock block(smaller bore) 512" deal. Same heads, same 2" carb, 13.5-1 compression, NO vacuum pump and it has been 9.40's in a 3300lb road runner. Of course its got one of those mystery power robbing slush box torque multiplier things behind it. I think the carb is killing it as well as the very conservative timing(locked at 26) they run. But the owner is 76 and as he says is going plenty fast enough for him.

What rockers do you plan to run? Pushrods? Installed hieght? All that combined with the life you expect out of your cam and valvetrain will need to be thought out thoroughly. If you want to push it, i have a 283/296/112 with .500 intake lobes and .460 exhaust sitting on my bench. I can send you a pic of the camcard

Switch to EFI and run a 2000 cfm throttle body. Worked for me.

Andy said pretty much my opinion.
I think 820 is pretty easy with the CNC 345 heads and a cam around 0.750" lift (1.6 rockers)

For some reason 2 barrel carbs and 4 barrel carbs are not rated the same way. The 6pack carbs come out to around 950cfm in 4 barrel rated numbers If I recall correctly

Hi Les, The 580 wasn't built as an all out effort but as a reliable low maintenance bracket motor, we've learned some stuff along the way and got it running good without loosing any reliability. You are correct, it's just under .750 net lift on the inlet and .730 exhaust with 1.6 arms (tempted to go to 1.7's but it just ain't that easy) It picked up some running low tension rings and a vac pump. We also found a couple of things at the end of the 2019 season so we may pick up a little next time out but we'll see.
The OPs engine should easily crest 800hp with a couple of tricks maybe 850, an all out effort and some real attention to detail should see 900hp IMHO

I run a 1050 on my engine BUT that’s acceptable to under carb a nitrous engine to get some carb signal when using larger amounts of nitrous . I would think a larger carb would help . But it is an easy upgrade later , and real easy to even borrow one and A-B test it at the track