All models of webber gasses are/were offered in lp or NG models. The main difference between the two is the size of the opening in the orifices on the burner manifold and side burner. NG orifices have a larger diameter opening.
The safest way to convert is do a full manifold swap either from a donor grill or buying a manifold. One difficulty here is that Weber won't sell you the manifold.
Another method is to replace the orifices with one's sized for what you want. But, there are some issues here. Weber used 2 different styles of valves. One style is continuous where there is a channel in the valve that gets wider. The other type has three holes, smallest being low setting, the largest being high.
Trying to remember which way this goes off the top of my head. If going from NG to LP, then there won't be much difference between low and high setting on a burner. If going the other direction, from lp to NG, then low setting runs lower to the point where it could blow out.
To my knowledge, no one has identified or documented which model grills have which type of valves. Best bet is to take a valve apart and see.
All the above said, I've converted 2 grills from NG to LP by swapping orifices and both worked fine.
Oh yeah, left out that when going from NG to lp, you'll need to get an lp regulator as well.
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