dual 2 is going to give you better distribution, but a 4 wont have to be balanced like a 2. If your using 2 new carbs, balance should be pretty easy, just make all the jetting and bleeds the same. 2 has linkage issue also. IF they cost the same, (they wont) I would go with the 2. if you go with a 4 try and find a 390 Holley or a <=500 carter. Some old OEM Carters were smaller than 500.
Badvert
Im guessing youre gonna run an automatic with a bit of stall then?
If you go with a 4 try and find a 390 Holley