Well I dont have a Losi but this how I installed it in my 808 buggy.
I used a ½ forstner bit and drilled down just until the bit penetrated the base holder, this allowed me to countersink the existing body screws into the holder and use a longer bolt with a counter sink ¾ washer on the top allowed me to secure the battery holder to the chassis. I also noticed that I could take the battery try and use my belt sander to takeoff another 2mm getting me to 39mm in deck height. I'm just not sure what the stock deck height number is?? Do you know??.
At its current location with a 5s 3700mAH on board it sits exactly 40.97mm (41mm) above the bottom of the chassis.
Hope that helps??.
Have a great one..