2 barrel to 4 barrel?

Here's a partial answer:
The throttle linkage rod will have to be lengthened at the carb - Edelbrock actually sells an extension for this. I'm running an Edelbrock Performer manifold with the 600cfm Edelbrock carb on my 318 and I had to weld an inch and a half extension into the throttle linkage rod to get the kickdown to work properly.

You can check this by going through the kickdown set up procedure in the Factory Service Manual. If you can't get it set properly with the linkage hooked to the 4 barrel, see if it will set up with the linkage disconnected from the 4 barrel. If that works, you will be able to see and measure the amount the throttle linkage rod needs to be lengthened.