The very first machined Delrin chassies were made just like a Losi XXX chassis, and the two front "arms" broke off on the first battery pack.  Greg did a great job gluing them back together and we kept testing, but for the second batch of fiberglass-filled Delrin prototypes we added lots of material for strength.  Notice the thick spot in the side of the chassis, as well as extra material on the floor in front of the servo.

Where I ground out the chassis, the point to this is so the pins of the servo mounts sit flush into the hole, servo as low as possible. Areas boxed in Red to highlight areas.

We added too much on the floor, and the Boyz had to grind off a lot to fit their servos.  When we made the magnesium chassis, we took away some material there, but a lot of grinding was still necessary.  We removed still more material for the production prototype molded chassies and held our breath.

Same grinding area, different angle....again, red boxes highlighting areas.

The Boyz still had to grind some, but no molded chassis broke. So we really held our breath, removed a bit more material, and went to production.  It's almost right, but we'll take more off in the second batch of production, sometime next year.

This picture is where the servo tabs themselves were slightly trimmed. Just enough to match the bottom of the servo mount, once again, so the servo sits flush. Sorry for the quality, I need to figure out how to use "macro" focus on my camera...or buy an easier one to use.

You get the best of both worlds.  By custom-fitting your servo, no more material than is absolutely necessary is removed, so your particular servo fits and the maximum material is there.  As this is written, no one has reported breaking a chassis there, so we think this is actually a good thing.

The tops of my servo "ears" were touching, so I trimmed them, and I trimmed the chassis in the spots shown (well I only show one). If you dont use button head screws...you may need to trim the chassis where the top screw is. I used button head screws on the bottom

Do it carefully.  It doesn't really take more than about five minutes, and you only need to do it once.  Follow instruction A4. 

We've included with this article some pictures from Joey King which show how he did it.

A bit more history:  At first there were only going to be six bags in the Kit, but we decided to have you do the servo first so nothing would be in the way while you install the servo.  That's why Bag G has so little in it -- G and A were supposed to be one.

Special thanks to X-Factory family member Joey King for the pictures.