Although, not a cloned car, to me a restamp is still a restamp - originality has been lost in the sense that there now is no way to prove that the restamped engine was original to the car. Doesn't matter that you know it is original, no way to "prove" it that I am aware of...and a car commanding high $$$$ needs documentation to justify the $$$$. I don't believe that restamping qualifies as documentation. To easy to fake. As you state - two shops that you know of that will do this. Will they only restamp original blocks or will they stamp anything?
If the car is put on the market at some time in the future, and it is clearly stated that the block has been decked and restamped, and the potential buyer acknowledges this and agrees, no harm, no foul....but if that fact is not mentioned, ......now we are into the arena of personal ethics.
Last year I finally installed the correct 327 in my '69RS. When I bought the car in 1991, it had the wrong 327 in it - a mismash of parts from a variety of engines. Over the years, I found the correct 327, pulled it out of a '69 Camaro that was being parted out, engine partial VIN and car VIN agreed, best information said the engine was original to the parts car. Date code was acceptable. I needed a FK code, this one was FJ (powerglide vs. 3 spd manual).
When I had the machine work done on the replacement 327, I fully documented (pictures) the pad stamp prior to sending the engine to the machine shop. I never considered a restamp. Kind of proud of the fact that the engine originally installed in a plain jane 3 spd coupe, VIN# 124379N551248; engine code V1122FJ, is now in my ride.
Whoever winds up with my RS after I'm long gone, will also get a plethora of documentation describing everything that I know about the car. Only being honest with the next owner.