1970 L78 Camaro Dilemma

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My brother and me are trying to figure out what to do with this 1970 L78 Camaro (VIN 571940) he has had around the house now for 6 years. It is a major project. Non original transmission and a non-original engine that, strangely enough, came out of another 1970 L78 Camaro (VIN 587606). No buildsheet but an owner chain that has been researched back many, many years with accompanying titles and names. Original COO 12-bolt with 4.10s

When he bought the car out of Ontario, Canada he was told that 587606 still exists as a shell but both the owner of the engine and the owner of the shell could not come to any agreement. The 587606 bodyshell was last in Columbus, OHIO belonging to some guy named Keith. So that's where that story ended.

Today he has this car with a non-matching drivetrain and in need of metalwork and restoration. I am of the opinion that what will need to go into the car will outstrip its value in the end, considering the reference "barn-find" green '70 L78 could not even pull 45K on eBay a couple weeks back. So he should be able to find a done car with matching numbers and some docs for 50-60K - theoretically. Problem is they don't come up for sale very often, especially matching numbers examples. And he just wants an original '70 L78 Camaro to own and drive and is not strictly concerned with value of the car as an investment, but at the same time does not want to get stupid deep in the car. So is he better off digging into this as a resto? Or sell? - and what is this thing worth as a project car in its current condition? Give me your honest opinion here on value of the car and what direction to take. TIA