Jim/Jom,
You only need to square the edges of the battery hole, top and bottom to make a larger capacity, higher C rated battery fit. It may actually give the chassis a little more flex and added stability with the battery being heavier.
A new MO5 chassis parts is not really that expensive. Also in Thailand they race open mini, with most using a 10.5 BL boosted system with speed gear sets, so extra voltage etc is better.
Remember not all play to our rules.
It is a diverse mini racing playground.
For this years TITC we are all using speed gear sets, with a max 24 tooth pinion, fixed time 17.5 motor and Critix SP ESC. About as fast as our 13T BL hobbywing setups, however the system is less demanding on the cars. The power is more evenly spread than the sudden torque of the HW systems. Weight limit 1200 gms. So some highly dremeled chassis do and will make it to the racetrack.
later,
Calvin.