Someone
has built this mousetrap, and you commented on the thread!
https://stunthanger.com/smf/stunt-design/three-surface-stunter/msg563418/#msg563418Remember that there'll be loads on the spar -- I think I'd make a carbon-fiber thingie that goes around the motor and has stub spars on it, to which the front surface's spars attach or continue.
If you do take my suggestion on the CF ring thingie, allow me to additionally suggest that you make the panels removable -- this will allow you to experiment with areas, aspect ratios, control ratios, weird asymmetrical airfoils, etc.
If it's right up against the prop you'll have extra prop noise. It may or may not be worthwhile to use cambered airfoils, arranged to straighten the air from prop -- this may actually add some useful thrust, by converting some of the slipstream's rotary momentum into backward momentum. If you don't want to build a separate set of panels to try this, you can try tweaking the control surfaces.
The best CG position will change.
Build a chuck glider and try it out. Use up some of that scrap balsa that's too heavy to build stunters with. Try it without the front surface, and again with. You probably want to adjust it for a fast glide, instead of the best HLG performance -- so build in some tail incidence. Adjust for the same sort of glide with & without the front surface, and note how much you need to change the CG to get it -- that'll be a first cut at how much you'll need to change the CG for the full sized plane.