G'day Derek.
Over the years that the Aquarama was in production there were several changes to the design of the fuel/water fillers.
Some of the early ones were almost flush to the deck with no fixing shown as the fixings were done from the inside, Riva usually preferred not to show fixings to as
much of the deck furniture as possible. Later in the production, especially with the introduction of the "Special" version, the flush versions were changed to the
larger Mushroom design there were 3 versions that I know of, all of which had flanges with external fixings but they varied in height and diameter.
I have made some of each type and have settled on the Mushroom design, but I have altered the diameter and height so that it looks right on my model.
Rightly or wrongly I preferred the 5 bolt flange fixing, so that is what it will have, after all, my model isn't perfect scale, far from it, also, some parts cannot be scaled to
1/7th ish, they would look silly and I try to avoid silly where possible.
The previous post was intended purely show how I achieved perfect hole spacing.
Thank you very much for the technical information tho', but fortunately not needed in this case, maybe in the future.
Mike.