The only way to get this to work, would be with the people who are target "consumers" to become "Investors"...that way the risk is shared as well as the reward.

If 2 years down the line and some of the castings start to crack or have any problems, the "Investors" realized that going into an investment to get correct manifolds for their cars and could contact the manufacturer (company that casted) them directly, or take them to a machine shop and repair them on their own dime.