With the machining possibilities available to you, it should not be difficult to modify the original manifold.
Obviously a new manifold will be more efficient but you put your finger in a dangerous gear, the race for power because "we" and you will quickly say to yourself that it is a shame to keep the original camshaft with a collector and a carb capable of doing much better and then even if it means putting in a more efficient cam, you have to change the rocker arms, etc, etc...
It is with this kind of progression that I found myself one day adding 200 hp to an engine that was already producing 420 when at the start I just wanted to replace the clutch which was worn.