2bbl to 4bbl what kind of power increase

I finally found me a good running 71 318 Dart. Factory stock except dual glass packs with 45,000 miles. It has the Rochester 2bbl carb. I have an Edelbrock LD4B manifold and old Holly 650 sitting in the shop.

On a stock motor what performance gains might be seen by changing over to the 4bbl. If it's not much I'm not going to bother with the trouble and just sell the intake, but if it's a noticeable gain the hot rodder in me has to go for it.