Cherubini deck construction
The picture shows the deck section on my 79 H33, made up of end grain balsa, with fiberglass layup top and bottom. In addition, the cabin liner was more or less glassed into the lower layer of the deck section, perhaps adding additional flexure strength. Selected sections of the deck requiring more screw pull out strength than the end grain balsa would afford, e.g. under handrails, have the plywood core. I remember Sam Lust with one of the last H33s saying that his core construction seemed to be plywood throughout. It may be that the construction techniques evolved and changed with balsa giving way to plywood in the later years of the cherubini construction.