Tynecastle,
The "data" you are quoting is not very meaningful, unfortunately. The fuselage strength and crashworthiness of the 61 is significantly less than the 76, and than the 92, or the most current part 29 aircraft.
I know of several very hard landings with 76's that would have split open other helos (I am the proud author of one of those). This is not to say that a 76 is superhuman, just that your means of comparison is drawn from warstories and suppositions.
The boat hull on a 61 is a nice feature, but it does not add significant strength to the fuselage. Where did you get that idea?
The concept you wonder about (the protective cage for racecars) is exactly what I described in the previous post. The "cage" of an S-76, an Apache, an S-92 and (probably) an AB-139 are about twice as strong as an S-61, Super Puma or EH-101. This is determined with data, not suppositions.