I just sent a roll off to Dwayne's yesterday. The prices are the most reasonable I've found, and it's where Kodak sends you in North America, while a lab in Switzerland is for Europe. I'll post my results once I have the film back.
Just to be clear, though: there was no Kodachrome 64 in the WWII era. It was just "Kodachrome", and the ASA was 10, IIRC. Somewhere I have a Kodachrome print (yes, there was a Kodachrome print material at one time) from my parents' wedding (ca 1947) and it looks very nice. The colours are more muted than what we think of as Kodakchrome, but I don't think that has much to do with fading, but more with how Kodachrome looked at the time.
Agfa had invented a commercial/consumer colour material around the same time, but with the result of WWII, they never could achieve market dominance on a global basis.
Trius