The two aircraft are registered as N926NA and N928NA.
From the FAA Registry, N926NA carries a serial number of 63-13503A. Looking at Joe Baugher's site, prior to conversion into the WB role, it was was RB-57D 53-3974. From Baugher, N928NA should have a serial number of 63-13298 (the N-number is listed as "reserved" in the FAA database) and he shows that it started life as B-57B 52-1536.
So to answer your question, they would have been manufactured in the 1952-1953 time frame.
KC-135: Passing gas and taking names!
Last edited by Moose135; 12-12-2011 at 05:06 PM.