I’ll just add this, as a reference on where you might need to end up with regards to ifr sizing.......

In my experience, when using cams similarly sized as what the OP is using...... if one had a normal Holley aftermarket performance carb that had the traditional 2 corner idle circuit....... like a 4777(650dp), or older model 4779(750dp, before they came with 4 corner idle), or a 3310(750vs), you would find that those carbs would have marginally acceptable idle circuit capacity(it wouldn’t be good enough to where I could leave it with the stock calibration).
And those carbs all had the fixed secondary idle discharge ports contributing to the fuel flow, in addition to having a more performance idle calibration(as opposed to the factory emissions calibration with a stock cam that provides nearly 20” of idle vacuum).

What I would do to solve the idle quality issues on those carbs in motors with big cams, where the rules didn’t prohibit it, is to install 4 corner idle....... which nearly doubles the idle fuel flow capacity.

You can’t do that for Stock....... but you could get creative with some replaceable idle feed orifices installed in the secondary side of the main body or baseplate.

While a std performance Holley carb with a normal 2 corner idle circuit would definitely be an improvement over the factory 383 carb in terms of low speed operation........ if you swapped it out for a carb with 4 corner idle you’d see how much better still it could be.

Right now, with the tiny ifr and lack of any additional idle fuel flow from the secondary side....... I’m going to say the low speed operation bar is set extremely low.