Andy The original model was produced in the early 1960s when IC engines were the norm and scale and RC for sailing models were in their early development stages. Supplies were limited and we made do with whatever was available. The plans were typically sheet on frame, probably plywood from an old tea chest and cascamite resin glue ( it was water proof and slow setting).
The designer would suggest suitable wood to use but many chose to use what they could acquire and as a result the finished models often finished up heavy or very heavy. Coupled with the large IC engine and flywheel and large heavy RC escarpments and big drycell batteries, it is not surprising that the hulls sat well in the water.
To the modellers of the period the waterline really didn't matter as we were after speed, control and endurance.
This may explain why the early plans did not show a waterline, as in my experience the draught varied greatly between models.
Today we have scale plans and supplies that allow us to build true replicas and all the important detail is a must for a true scale model.
Personally as an ex flyer I try and build lite, bricks tend to fall or sink, and my Sea Queen rides high in the water with a slight bow up. A 42xx brushless and LiPo add little weight and I have two 8oz lumps of lead in the stern section to achieve this.
If it looks right, sails well and you are happy, then enjoy your model.