For retaining the battery, you can either use the standard strap, filed down, or get a custom made one.
The weight balance will depend on your speedo and radio gear weight and the weight of you lipo as they vary. But chances are it will be a bit out of balance, you can get some lead under the radio gear and/or under the servo, and then many people add some either side of the spine. If you do a search on here there are some neat installs. Ashley's is a good one.
http://www.oople.com/forums/showthread.php?t=37780
Scroll down and you will see both types.
Good luck.
Chris