383 Wont Idle with new to me 800cfm DP. Idles and runs ok with Edelbrock/AFB

If opening the back barrels helped the idle, then I think you are spot on. You are band aiding a problem with your primaries. The transfer slots are important and yes, the secondaries are used in idling, but little. Should be mostly the primaries. Now I say one of 2 things, your primaries are not delivering any fuel till part way open, and that is why it only idled at 1800 rpms, or the primaries are delivering too much fuel, causing it to die unless opened up to 1800 rpms. This is very easy to tell, and the flooding would girgle it to a die. No fuel will be just that - like running out of gas. This would explain the idle jets not working, no fuel to work with... LOL