'morning..
I carefully peeled back the covering just aft of the wing saddle
I made a "hatch" by cutting into the fuse directly where the red meets the yellow just aft of the wing saddle.
By doing so I was able to get the battery pack on the under aft side if the cockpit floor, and I then ca'd in some 1/4 X 1/4 balsa sticks to secure the battery in.
Because the covering is Ultra I just ironed it back down and you cannot tell I was ever in there.
With my OS 91 Surpass the C.G was spot on..
I'm assembling another this week and I'll measure it with my C.G machine and let you all know.

I also have my engine back all the way...had to carve a wee bit of the mount away on the left side but it made a difference.
Be sure to add a few washers to counteract the torq of the Saito...Do it now, trust me you won't get a near vertical line without them.
And when your in hover every time you blip the throttle it will kick left.
I'm talking right thrust BTW.
Good luck,
Oh, did you reinforce the horiz stab? LE and TE top and bottom?