The Guillow's Corsair will be a fast plane with that sort of power. So while the single dowel and single screw will do fine you'll want to ensure a couple of things. First off is make the dowel large enough to do the job. 3/16 hardwood should be fine. Second is that the plate the dowel fits into needs to be plywood and extend far enough over enough of the bulkhead it mounts onto to transfer the load out and into the bulkhead, stringers and sheeting or planking used for the outer skin. 1/16 or even 1/32 would be fine as long as it spreads out the load. And same at the back end for the screw. The threaded block or plate should be glued to the bulkhead there and should spread out to the side skins.
Along the way you'll want to harden the wing's center rib by making it out of at the very least fairly hard balsa or plywood. Or band the center section with a 1" strip of 2oz fiberglass tape and epoxy to give a good strong center line strength. After all the center point of all the pressure is at a line between those two points. It's spread out but still......
It's also not as bad as it sounds since you're not likely to be doing really high G inverted stuff. The positive G loads will be taken by the wing saddle. Only any negative G loads will need to be taken by the dowel and screw.