Hello, Guy,
Your idea sounds good and I know that something like this has already been done with an exploding submarine and it also looks great.
Of course you can pour the model into resin up to the upper wing, let it harden and fill the rest with resin in a second session.
You should use acrylic glass as the casting frame, which you form into a box with an appropriate adhesive (e.g. UHU-Hart).
The only concerns I have are air pockets that collect under the wings or in the fuselage and remain visible in the resin during hardening. You will also need to use a resin that is highly viscous, shrinks minimally and does not get hot during curing.
Maybe you should test it first with a cheap, unpainted model.
Bye,
Manni