+1
Thirty years building/buying/selling/trading basses, here's my take on the whole "buy something that has the look and upgrade" philosophy:
By the time you invest the money, time, and energy to actually land a decent, playable copy and then upgrade it to attempt to match the original in all respects, you will have a financial investment close to the original, and you will still pretty much miss the sound and feel of the original.
At around $1,500.00 for a gently used 4003, I can't understand the desire to circumvent buying the real deal, especially thinking you're going to somehow come out ahead or buck the system or whatever. If you truly like Rics, you will only end up disappointed.