Not trying to be a smart-azz here... but what is the actual need for a safety loop on a shaft 20" long?
(Maybe a strap across the tunnel under the front U-joint, but a full SFI loop? As someone who has snapped one on a "full size" car, and sheared a pinion shaft as well, I know the need with a 5 foot long driveshaft...)

I'm thinking more a scattershield in the U-joint "fling" zones... .040 aluminum between me and 5000+ rpm shrapnel isn't healthy.