If you will be adding a Flex-Drive, you will definetly need to remove the stock-driver in the pill that is pressed into the battery-tube.
In my last few DJR-builds, I have removed the stock-driver board and removed all of the componets from the board and replaced it in the pill. This way the spring coming from the FD "+" can rest against the old-driver-board instead of directly against the top of the battery. The battery in turn now pushes against the contact-board instaed of directly against the spring that is connected to your FD and diode, less stress.
Also, if you are using the DJR Full-body heatsink, the little black-plastic cover for the stock-driver pill, will fit perfectly into the back of the Full-Body heatsink to help support the spring and close-out the back of the heatsink.
Barry