corky... The answer to your question is somewhat dependant upon the types of tracks you will be running on.
If you're only running on tracks that are smooth with lots of turns and very few and/or smaller types of jumps.. then drilling the chassis to prevent the clutch bell from making contact may not be needed.
On the other hand if you're running on rough tracks with a lot of big jumps or extreme whoop sections then you will probably find this mod to be beneficial.
The best way to know if its necessary for you is just run your car without drilling the chassis and keep a close eye on the clutch bell and the area of the chassis directly below the bell for signs that contact is occurring during extreme chassis flex situations. It will be obvious and easily spotted.
This is what I did with my first chassis... now I just drill/dremel them before I build 'em.
Good advise, thanks mate.
The tracks i drive differ, some smooth, some rough.
But i'll do exactly as you said, just keep an eye on it for the time being.
Thanks mate..