We have the original 208 ignition coil on our 65 Nova (194 C.I.D 6 cylinder) but not sure if the secondary resistance is up to par.

Engine runs ok... spark not yellow... doesn't seem to leak any oil.
Primary is spot on at 1.5, secondary is 5.9K.
However the specs on the replacement coil are 1.5 and 12K (min 7.5K).

Does this indicate the original coil is living on borrowed time and should be replaced?

My former 1934 is still doing fine with the original coil.
If you don't have a problem don't worry about it. I always carry a spare coil in the trunk of all my cars.

That's what I was thinking. The replacement is already on, so the 208 can go in the trunk. It should last longer in there. At first I thought it went bad but that turned out be me never realizing you really can put the diz advance weights on backwards.
It was like driving a herd of turtles going up hill :)
Spitting and popping all the way... all's good now.

My all original 1932 Special Sedan is still running with the original coil. If it ain't broke, don't replace it!

Very true but sometimes determining what's marignal is not easy to discern. 6K was the lowest spec I found, so being under that, didn't inspire me with confidence in the coil. I guess, other than leaking oil, there is no warning - they either work or fail.

Some modern ones overheat and cut out. After cooling they return from the dead. So you might not be better off replacing one that is working even if it is old.

I have heard that's possible, probably even with a oem coil. On the 1,000 mile drive home from purchase it may have done that twice but then there wasn't much time to dig deeper. There was a lot of "deferred maintenance" on this car I've been sorting out on and off for about a year, so everything is suspect until proven good.