Two Barrel to Four Barrel Upgrade?

I've done this deal also, with a Holley 600 cfm vacuum secondary on a 70 Dart 318 that was stock except for headers and dual exhaust. I used a Weiand single plane intake when I put the 4 barrel carb on as well. I found that the 4 barrel required about the biggest accelerator pump shot available to get the engine to not stumble, but tuning that variable and when the secondaries came in made made the car a LOT faster than it was with the tiny 2 barrel it came with. I eventually went to 360 heads, a decent sized cam and a Holley 750, which again made a big jump in performance at the cost of some drivability tradeoffs. Your carb isn't too big, but it does need to be optimized for your car.