The primary function of the intake manifold is to evenly distribute the intake air to each port in the cylinder head. Even distribution is important to optimize the efficiency and performance of the engine.
The stock intake manifold has been dyno proven to flow more stock vs. stock when compared with the Quad 4 HO intake manifold, however this greatly changes once forced induction is introduced. The stock intake manifold can handle moderate amounts of boost pressurization, but being that it is constructed from a plastic, it's integrity may be compromised. Some have had theirs break into pieces upon adding too much boost or having a wet nitrous system puddle in the manifold and ignite. If you're looking into adding much more power, the stock is not the intake manifold you want to use.
Porting the stock plastic manifold is generally considered a waste of time. It flows good enough as is, and there is not much material to port; attempting to widen the stock manifold is useless. Otherwise, you use a dremel or porting tools kit available online.
Lots of modifications must be handled to fully benefit from this swap. The key and most essential modification would be the intake manfold's flange. The LD9 Twin Cam and LGO Quad 4 engines each share distinctive cylinder head intake ports. Thus one must modify the manifold for a perfect fit.
This can be accomplished with three options.