Ok everyone, once again thanks for all of your suggestions! GOHZU, I took the strong recommendations for the Racal Dana into consideration and found a spotless 1992 1.3 GHz unit with the OCXO option (04A) for only a few bucks more than the HP would have been, and this counter was in better shape. Seller indicated that all the switches were in good working order, with good tactile feel, and he showed it hooked to an Agilent sig gen and an Agilent counter for comparison and also hooked to a GPS time base, and it all appeared very well within spec.
I've saved the info on the HP, however, regarding fans and that pesky relay in case I later change my mind. The discussion here has been VERY helpful, and I've learned quite a bit along the way (which is why I'm doing any of this at all... learning).
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"Catch ya next time!"