Lots of things to think about here......

I've got a Sturdy Birdy so I know roughly the hardware layout...

1. If you mount the 2nd wing under the fuse you ain't gonna get the 1 chord distance mentioned earlier...

2. You'll have to cut through the wing and mount the servo on the bottom and use new hardware or pull the ailerons and swap the torque rods..

3. You need to build a support for the bottom wing to ensure that it has the correct incidence

4. You'll need some sort of stagger as the wings will be close, then you'll have to figure out the new CG, tricky as there is virtually no scope for moving things around in the fuse when it all taped to a rail...

The easiest way by the looks of it is to mount the wing just forward of the main gear, then the CG will need to shift forward a bit. One way to do this is to put a bigger engine on front

I wouldn't bother to change the gear to a tail dragger. The SB is a taildragger and it's a real handful on the ground..