[304065]

Here's a guess:

Aluminum has an approximate density of 2.70 grams per cc.

104 pounds of aluminum weighs 47,173.6065 grams.

47,173.6065 divided by 2.70 = 17,471.28 cc of aluminum in the frame.

Now, if you assume identical tube sizes, the less-dense magnesium frame would weigh 1.738 grams per cc, which means the frame in magnesium would weigh 30,365.863 grams, or 66.9452685 pounds.

Let's call it 67 pounds, shall we?

Of course this doesn't take account of the additional material required to make the magnesium structure work the same as aluminum, but you get the idea, right?

On the other hand, I bet the car was slower because the driver was afraid of doing his impression of Dresden. . .