RE: fuselage length
A lot of your re-design considerations can be worked out with the help of the geistware.com application.
Moving any tail back improves the leverage it has for controlling the pitch and yaw (if you move the vertical stab and rudder with the horizontal surfaces) control. Precision flyers moved the empennage back in the days when smooth was what scored in their pattern and moved it forward when snaps were important.
3D mostly depends on larger than usual surfaces but a longer tail moment would let you reduce them somewhat. Bottom line is that for 3D, too small won't do well. Extending the tail as you think will do what you expect.
The CG won't be a problem for your new plane. Use geistware and you'll get absolutely reliable and exact location for whatever you wind up with. No need to debate the issue, find out exactly based on your exact measurements.