Is this in a truck or a passenger car?
Does the engine (the air cleaner in particular) look like this?
View attachment 1716429656
If it does, you're in for a lot more work than a simple manifold swap. That's a second generation (post Lean-Burn, but similar) engine control system, which utilizes feedback signals from the carburetor for fuel management and a locked distributor that relies on the computer for an advance signal (note the vacuum advance can on the air cleaner mounted engine controller).
You will need to change out the ignition and do a fair bit of rewiring in order to eliminate the rudimentary computer system and get the engine controls and some of the instrument panel warning lights and/or gauges to function, as well as deleting some of the pollution controls which will be inoperative once the computer is eliminated. And honestly, I forget if this iteration of computer controlled the charging system or not; so you may also need to wire in an electronic voltage regulator circuit with no computer.
If you're talking about a truck, much of this may not apply (depending on the model/ weight rating), and may lend itself to this swap a little more easily.