There are probably as many Sprint replicas out there as real Sprints. Manifolds are easy to come by and you can't tell the head is a Sprint head without pulling the Cam cover. You can tell if the block is a Sprint block but you cannot tell in 1967 if the motor is original because they didn't stamp serial numbers on them only the EID. If it has the original POP (not very likely) you can also tell because the EID is on the POP. Swapping to a 4 speed is also easy, just did it in my Sprint and you would be hard pressed to tell. That said, the condition of the body is probably more important.