Some querying determined the Prologic had reverted to Controller mode while the 2713 was in Talk Only mode. With this corrected, a Plot button push on the 2713 once again sends the screen graticule and trace info via Prologix USB to PrintCapture, however: there is no readout data printed, just the trace and a virtual graticule. Querying the 2713 diagnostics shows GPIB test Failed. Interestingly enough, the real-time clock does not update when the 2713 is turned off, even though both backup batteries have been changed. Both of these failures appear to be located on the GPIB board...
I'll continue to try and find a common issue, but the offer to purchase a known good #671-1859-0 GPIB board stands!
Howie / WA4PSC