Best aftermarket intake/carb for 340 V8 '67 CUDA?

Your stock intake besides on being heavy isn't a bad intake. Sounds like you need a new carb more so. Holley /demons make more power-the double pumpers for sure yet I like the Carter / Edelbrocks for daily drivers since they seem to love idle and low rpms more than the Holleys.

If it was my motor I would just swap the carb out and see how much better it is. Less work and money.

BTW, I am using a rare D66 dual quad intake on my 340 with two 500 Carters. I love it! Motor fires right up cold and idles cold after just 20-30 seconds of running. My old Holley and then Demon carbs hated cold motors and I tuned it, believe me. Played with the air bleeds and idle feed restrictions. Made it better but never as good as my Carter carbs.

Yep, I would just drop a 750 Edelbrock on it and nothing else and go from there.