It's been a few weeks since I received the new coil and TCI box purchased off of Ebay. The coil wiring connections are different and will require new connectors, the TCI box appears the same as the "performance" one I purchased from CM a year or two back.
Before trying any new parts I checked all the wiring and connections of the ignition circuit. All seemed well so I checked for spark and on this particular morning it was home! Fired the bike up and watched it idle peacefully for a few minutes and suddenly it quit. Pulled the plug and no spark! I quickly installed the new TCI, easier and faster than changing the coil, and the spark reappeared, stronger than before. Took it for a short ride, hoping for the best, expecting the worse, and it continued to run.
I was able to extend my ride this morning to 50+ miles and the bike ran normally. There is an occasional hickup when rolling the throttle on at a low speed which may be due to carburetor adjustments, but I'm happy to be thumping along at 60-70 mph.
Is there was a way to diagnose TCI failure? Felt like I was shooting in the dark when I bought the new unit, but ended up hitting the target. Certainly worth the $27 for the box and coil (which I'll likely need sooner or later).
Thanks for everyone's input and may my experience help someone down the road.
Bill N.