It sounds like you are questioning whether you want an all original, documented COPO vs one that isn't. It also depends on your financial situation. If I wanted a COPO car for a collection, it would have to be a documented, numbers matching car. The only questions would be color, transmission and extra options. From there it gets tough between a documented car with non original engine or trans vs a supposed numbers matching car with no documents. There is so much restamping and fake documents going around now that I would have to take it slowly to make sure everything looks legit. I wouldn't even want to begin to put prices and deduction on certain combinations since that is a personal thing. As for the transmission, I think you'll be very surprised how a TH400 in a COPO runs so that wouldn't be a value deduction at all to me. Sleeper = 427, dog dish hubcaps, auto on the column, no fancy options.