Plan on about $4500 - $5000 for all new parts. If you have the transmission, that will save you about $1400. If you have the pedal assembly, that will save you another $300. I can't say for sure if the auto trans console will work for a 4speed. I would guess, at the very least, you'd have to get a new top plate to accept the 4 spd shifter.
I just did this on my '69 Charger, and will attach the list of parts I needed for mine. I've heard of others finding all the parts used for about $2500-$3000, but it took them a while to round them all up. I have gotten quotes from Brewer's Performance and Passon for all my parts. I went with Brewer's because they were a little cheaper, and were within driving range to pick it all up to save the shipping freight.
Your A-Body will need some different parts than my B-Body ( i.e.... I know the torque shafts mount differently), but overall it should be pretty close. Here is a parts list I copied from my quote from when I just did my Charger.
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