Welcome to the forum, Tim. I'll try to save words, is why this will look presumptuous. I'm just considering if it were to be my own offices, and trying to save on installation costs.
You mentioned 14 ohms. Was this a ground rod test? If so, it's okay because you need LESS than 25 ohms. In theory, the steel in ground rods deteriorate with time and can be added to with a new one, bonded to the first, per 250.56. This is the 'ground' from the grounding strip at the service entrance. If the 14 ohms you mentioned means a metal box back to the panel along rigid pipe, it sounds as if the serrated washers need to be knocked back in before proceeding.
What you want to get for your customer is performance. If the wiring has been done in rigid pipe, you have an acceptable grounding path installed; what am I missing here? The GFCI is there for personal protection, not for clearing faults. My 2002 NEC handbook has a photo inside the front cover "bonding jumper not required" and attaching receptacle ground to metal box pictures in 250.8. My neighborhood was wired this way in 1947 using steel flex as a ground conductor and I haven't heard of any problems.
The way to test the wiring is by performing a high pot test. Done properly, this will test the conductors and the ground path back to the panel. Better value for money than adding in appliances which would mask actual wiring problems, and it should be done anyway every ten years or when this type of wire is being worked with. This is the final check, even when using new wire.
If someone gets a warmer fuzzier feeling from 6 mA ground fault protection (not a bad idea, in my opinion) then by all means either find GF breakers or replace the first receptacle on the branch with a GFCI unit as Charlie pointed out. I've used GFCI receptacles with wiped out old power tools, outdoors, in bathrooms, etc. Each printer, copier, etc., does contribute to small leakage currents to ground, but there's no reason to expect any nightmare service calls because of them.
