OK, finally got the wirers, switch, battery, esc and timer to fit and be replaced in the field. Needed to add a hole through the firewall former. This allows the wires to loop back and through the hole and the battery sits flat with two Velcro straps with an additional Velco pad on the floor plate to secure for-aft movement of the pack. With this arrangement I can even get an 5S 1800mah pack if needed but the 5S-1600 seems to be enough and is about 1/2oz lighter.
Now got to get the rest of the stuff installed.
Best, DennisT