5kg static weight is 15kg when rotating

I'd be concerned that the supplier quoted it's strength in horsepower?

The force thats going to be applied to it is torque and only torque. Havig said that I know of a few cars that have been developed with a large diameter hollow alu propshaft, I think it was a Porshce engineer who initially perfected it in the early eighties, then came over to work for Ford on the RS1700t

However not knowing any of the dimensions etc who's to say what will work and what wont!