carb tuning help

Not close and it will run dirty with that initial. Anything less than 20 is going to be a huge compromise.

Don't drive it, but, turn the distributor advancing it until the engine has a hard time cranking and back it off just a bit. Start it, readjust the idle speed and see where you end up. You WILL need to make a bushing to limit your MSD distributor, or buy one.

I run stock 340's at ~15*, no way that 383 is going to like the same for initial.

254 at .050 is even more than I thought... 24-26 initial and the rest mechanical. Minimum idle around 1000-1100