How much chassis stiffening needed?

Swinger 340 said

Just seen a video yesterday with a 64', 1,300 HP Comet, missing everything you mention here. $204,000 and 23 years invested and only a lap belt. First time out he rear ended a SUV at a red light, due to brake failure. Both occupants were severely injured. Had they had a harness they would of been fine injury-wise, financially, no.

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It WAS a nice car, but if you're not gonna put a cage in a 1300hp car, why build it? To go for groceries and burgers at in-n-out?
There is a 40 Willys that I see here at shows occasionally. 10-71 blown 604" Arias hemi chevy...... with lap belts. Since no one will ever let him race it, why build 1600hp? Wouldn't 650 or 700 do just as well for a trip to walmart?