I take it you have some inside info that tells you it is all original?
We've recently seen a similar deal on a 70 Challenger 6 pak car that someone cut up as well and converted to a chevy LS, of all things, in the simple name of expediancy for the build.
My take on this is that we don't know all the details around some of the decision process to head down this route, which could be mixed vins, rebodies, etc, and not the least of which is some poeple flat out don't care.
How much better are these set us, it depends. IMO, many of these are simply subscribing to the "its new therefore better" principle. IMO, many of these drivers would be hard pressed to make these coil over set ups out run a vintage trans am car, which were on t-bars and leaf springs. Further proof of that was seen in the recent PHR street car of the year contest where the Hotchkis Taxi on their TVS system came in second plece in the autocross, besting a large number of purpose built, coil over sprung Camaros with 3-4x the money in the suspensions.