The "torque and horsepower" are not so much affecting the frame but rather the differential and trans. There is no added weight to speak of. There is some additional stress on suspension. But what do big engines do? Just make you go faster. If you will be doing the Baja or Heavy Duty drag racing, you can't use those frames. The motor is isolated by rubber and so is the trans, you should not box a 56 frame. It needs to, and is engineered to, flex. Never heard of an HO SBC or BBC breaking a TF frame. If you want to lose the originality of the truck, that's your decision. A modern chassis will give you modern safety and such and is, in fact, called RestoMod. Original era body with modern drivetrain/chassis. Then it can be truly said: "It ain't your Grandfathers truck".
