I'm thinking about doing this on my 68 Charger which was originally a 383/2bbl/4 speed with the stock round snorkel air cleaner and it will be getting a Holley 770 4bbl carb. I'd like to retain much of the original appearance so I'm needing advice on how to make this adaptation.

Find a drop base air cleaner clearanced for the Holley floats; usually cheap at swap meets, $10-$20. Use filter height & diameter (diameter will likely be 14") you need, and put the stock lid over it. Add a nipple for the crankcase vent hose. Done.
If you need a smaller diameter, they exist but not often in drop-base style.
You might have room for a standard base, depending on your intake.
Or find an OEM bottom that'll work with your lid.

Check and compare the filter for the 2bbl and 4bbl application , the non unsilenced air cleaner assembly , the filter MIGHT be the same , if that is the case all you need is the AVS 68 base .

Otherwise it shouldn't be hard to do what you propose, but I would make it like the unsilenced , meaning there is an opening between the OD of the filter and the top to give you the airflow you need .

Thanks. I should mention, as stated above, that I'm using an Edelbrock dual plane manifold (the one that looks stock).

Like said above, just use a drop base 14" with whatever height air cleaner and the 2bbl lid. works great, I've got one on a Holley 950.

Where's a good place to get a drop base?

AdvanceAutoParts is where mine is from.