Stock 318 bolt on performance modifications

For low rpm cruising, the 2 barrel is fine. Most Mopars came that way for a reason. You could theoretically get a little better mileage with a small 4 barrel carb, but only with a dual plane intake. You wouldn't notice the 4-barrel horsepower unless you scream the engine (>4000 rpm), and doesn't sound like you care to drive like that. I would put the motor in as is for now since changing the intake isn't any easier with the engine out than installed. Wait until you have the money and know exactly what you want to do. EFI would give you the best driveabilty and mileage.

If the V-8 engine harness plugs directly to your slant bulkhead connector, I would keep the Mopar ignition as is. If you must hack up the wiring harness, I would consider wiring in an HEI module and better coil. The ready-to-run HEI distributor is simple and inexpensive.