On my first SSE I left rudder & ele stock standard & only tweaked the wing mounting setup & sheeted the turtle deck.
Big mistake leaving the rudder cause she will always sink in knife edge.

On my second SSE I modified both ele & rudder.
The rudder I added 50mm (2 inches) to the trailing edge & counter balanced the top by removing the top section of the fin about 15mm above the hole where the tail wires bolt to.
I added 25mm (1 inch) to the trailing edge of the elevators & counter balanced them by removing 25mm from the horizontal stab, filling the gap with some scrap.

In hindsight I would not extend the elevators at all if I was to build another, just counter balancing them would have been enough for my flying style (I loath 3d rubbish sucking up the centre of the runway making fly bys impossible)

One thing to remember, if you extend the rudder & CB, the tail becomings a wind sock and makes taxiing a pain unless you have a strong tailwheel, mine wouldn't taxi in decent wind without doing donuts.

Hope this helps.