HELP! 66 cuda idles fine, but not when in gear

Challngd73 said

That was a great read. Makes sense and appears(hopefully) my main culprit for a couple issues is vacuum lines hooked up to the complete wrong spots. My brakes don’t have great vacuum either and seeing as it is not on manifold vacuum, that might be the reason. Can’t wait to switch these vacuum lines after work and see the results. Thanks everyone and I’ll update when I’m done!

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Unfortunately its wrong. Its not even factually true.
Go look at '67 or earlier shop manual. Then go look at a '68 and newer.
Or do a search here. I've posted this stuff before.
All that is irrelivant to solving your cars issues.
Use whatever it takes to get the timing neccessary for the conditions. The goal is maximum power through the angles of maximum leverage on the crank.

You can crutch it idle with adding more initial using the manifold vacuum. The question will be if there is enough vacuum in gear to get away with it.
Don't add more timing than needed to get a relatively rich mixture to burn well.