That's an original Indespension roller coaster, from what I can see. They used to make them like that about 20yrs ago - independent suspension units, mounted to a v cross member. This was prior to them fitting the full beam torsion axles.
To be honest, you'd likely be fine just using a bit of square box, as the hull would likely clear the cross member, due to the swing cradle rollers. If its a bit close, just raise the rollers.