The OEM dual plane gives me 18-19" vacuum here at 4,000', and the Holley is factory set up with staggered jets. My added O2 sensors say it's running pretty even so I have no inclination to mess with the intake side.
Also, my carb builder Rick Walker (who worked at Dodge) recommends leaving it alone. I'd consider EFI if anything.
Like mgoblue9798 in the SP2P thread here, I'd like the 413 to turn ~2,300 rolling the interstate, whether it's with an OD, or 3.71 Dana ratio. Right now its 3400 @70 with the shorter, new 19.5 radials and OEM 4.55...