Okay, "Hoods" are the rubber covers that go on the LEVERS. So, you say you got new 105 "Hoods", do you mean new levers? What kind of brake calipers? How old? If they're from 1989, they're probably single pivot, which aren't the greatest, and if the pads are the originals, they're probably hard, and could be replaced with new ones.
There's a possibility that if you've got NEW levers and OLD calipers, it's possible the levers don't pull as much cable as the calipers need. Mixing eras doesn't always work well. If you have modern levers, you might try getting modern calipers.
But, yeah, what cxwrench said is correct - fitting disc brakes safely requires a ton of work, and I bet you could solve the problem with new pads, cable and housing, or new calipers. Good pads on clean alloy rims should be able to skid both wheels without Hulk-like strength.
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