Hi Paul......you certainly have a few quanderies
1. Some builders would consider a sizeable block of balsa ...say 3" x 3" x 10" & shape the bow profile FWD of frames A, B & F
p2. This would then provide a surface to plank to.......
However from your image 3728 [incorrectly proportioned glass hull] indicates the flight deck is near parallel in beam from FWD of frame A >>>>>>>> back to frame B3
I am also assuming from frame A to F
p is the chain locker.......and F
p back to frame 1 1/2 is the forepeak water ballast hold
3. The support for the concave planking up to flight deck level could also be achieved with a pair of mirror reverse curved blocks shaped again from 3" x 3" laminated balsa blocks
4. You may also consider a smaller balsa block laid on the axis of the existing keel plate from A >>>>>>>> back to frame B3 to inset the lower planking into.......
Keep us posted.............Derek