When I built my Senior I wanted some agility (ha ha), skydiver drop capabilities, and towing power.
So my mods were:
Saito 120s
A skydiver opening
Tow hook release
Double sized rudder
Double sized elevator
The double sized rudder lets the plane do neat flat spins from idle to full rpm.
Here's some pics of the senior at the bottom of the attached page below.
http://www.rogue-eagles.com/joestagg/SKYDIVE.HTM